Unix socket support

[AdamantGarth]

Is your feature request related to a problem? Please describe.
Dropwizard seems to support unix sockets, but attempting to use them in Commafeed's config.yml results in an error:

io.dropwizard.configuration.ConfigurationParsingException: config.yml has an error:
  * Failed to parse configuration at: server.applicationConnectors.[0]; Could not resolve type id 'unix-socket' as a subtype of `io.dropwizard.jetty.ConnectorFactory`: known type ids = [http, https] (for POJO property 'applicationConnectors')
 at [Source: UNKNOWN; byte offset: #UNKNOWN] (through reference chain: com.commafeed.CommaFeedConfiguration["server"]->io.dropwizard.core.server.DefaultServerFactory["applicationConnectors"]->java.util.ArrayList[0])
        at io.dropwizard.configuration.ConfigurationParsingException$Builder.build(ConfigurationParsingException.java:277)
        at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:177)
        at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:94)
        at io.dropwizard.core.cli.ConfiguredCommand.parseConfiguration(ConfiguredCommand.java:139)
        at io.dropwizard.core.cli.ConfiguredCommand.run(ConfiguredCommand.java:85)
        at io.dropwizard.core.cli.Cli.run(Cli.java:78)
        at io.dropwizard.core.Application.run(Application.java:94)
        at com.commafeed.CommaFeedApplication.main(CommaFeedApplication.java:275)
Caused by: com.fasterxml.jackson.databind.exc.InvalidTypeIdException: Could not resolve type id 'unix-socket' as a subtype of `io.dropwizard.jetty.ConnectorFactory`: known type ids = [http, https] (for POJO property 'applicationConnectors')
 at [Source: UNKNOWN; byte offset: #UNKNOWN] (through reference chain: com.commafeed.CommaFeedConfiguration["server"]->io.dropwizard.core.server.DefaultServerFactory["applicationConnectors"]->java.util.ArrayList[0])
        at com.fasterxml.jackson.databind.exc.InvalidTypeIdException.from(InvalidTypeIdException.java:43)
        at com.fasterxml.jackson.databind.DeserializationContext.invalidTypeIdException(DeserializationContext.java:2040)
        at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownTypeId(DeserializationContext.java:1590)
        at com.fasterxml.jackson.databind.jsontype.impl.TypeDeserializerBase._handleUnknownTypeId(TypeDeserializerBase.java:298)
        at com.fasterxml.jackson.databind.jsontype.impl.TypeDeserializerBase._findDeserializer(TypeDeserializerBase.java:165)
        at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer._deserializeTypedForId(AsPropertyTypeDeserializer.java:151)
        at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer.deserializeTypedFromObject(AsPropertyTypeDeserializer.java:136)
        at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserializeWithType(AbstractDeserializer.java:263)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:361)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:244)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:28)
        at com.fasterxml.jackson.module.blackbird.deser.SettableObjectProperty.deserializeAndSet(SettableObjectProperty.java:44)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:310)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:215)
        at com.fasterxml.jackson.module.blackbird.deser.SuperSonicBeanDeserializer.deserialize(SuperSonicBeanDeserializer.java:120)
        at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer._deserializeTypedUsingDefaultImpl(AsPropertyTypeDeserializer.java:226)
        at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer.deserializeTypedFromObject(AsPropertyTypeDeserializer.java:145)
        at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserializeWithType(AbstractDeserializer.java:263)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:138)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:273)
        at com.fasterxml.jackson.module.blackbird.deser.SuperSonicBeanDeserializer.deserialize(SuperSonicBeanDeserializer.java:155)
        at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342)
        at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:4875)
        at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3033)
        at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:148)
        ... 6 more

Describe the solution you'd like
If it's easy to enable Dropwizard's support for unix sockets in Commafeed, I'd like that :)

Describe alternatives you've considered
Regular TCP sockets are fine, but not as tidy as unix sockets for my use case.

Additional context
I want to run Commafeed using systemd's socket activation feature. This requires opening multiple ports, as Commafeed (I assume) doesn't support systemd socket activation natively. One port is for Commafeed itself, and the second one is for socket-activated proxy). It would be neat if Commafeed's port could be a unix socket instead, hidden in commafeed directory, instead of being a second global TCP port.

[Athou]

Dropwizard unix sockets support was in a separate dependency. I added it in 34db9ba could you try again please (either from sources, with the jar that was built here, or the master Docker tag)?

[AdamantGarth]

Tried the jar from CI, worked like a charm. Thanks!