Configure port and host of the server

[w0rm]

I need to dockerize cosmos, but I can't, because it only listens on localhost, not '0.0.0.0'.
What would be a preferred way to set port and host of the server? I am willing to work on this feature.

[ovidiuch]

I prefer the config more than the cli args. Out the back of my head, I'm thinking:

1. Abstract the getUserConfig part into a lib so that it can be reused
2. Use it in the bin file to override the localhost:8989 settings
3. These settings could be set under userConfig.server.[hostname|port], except they would be just properties and not a method like the webpack config (hopefully it's not too confusing to be different)

What do you think? I'm open to other suggestions as well.