Mock APNS Server as a separate maven artifact

[saumitrabhave]

Guys, great job writing this awesome library...

Not sure if this has been discussed previously, but it would be really great if the MockAPNS server can be released as a separate maven artifact,

1. It might reduce some classes from the runtime.
2. It will be helpful for people using some other ways/technologies to send APNS pushes, but still want to use pushy's MockServer in their integration tests.
   Thanks

[jchambers]

Even though I didn't explicitly call it out, this will definitely happen as part of #459. Thanks for the suggestion!

[jchambers]

Now that we've dug into this a bit, I think I have a clearer picture of our options.

ApnsClient very much depends on the mock server for tests. To avoid a circular dependency, that means that the server module could not depend on the client module. Because we're publicizing more of the mock server, there are an increasing number of classes shared between the client and server, particularly related to keys and authentication tokens.

I think the only way forward would be to create something like a pushy-common module, but I'm not sure if the added complexity justifies the benefits. Having a few extra classes around isn't the end of the world, and having the client in the same module definitely shouldn't block people from using the server.

I'll think on it, but there are costs either way.

[jchambers]

I think we're going to have to defer on this for now; the main motivation for moving the mock server into its own module is developer convenience, but it turns out that's also where most of the costs lie. Let's keep looking for opportunities to make this happen, though.