Allow Aphlict to load Javelin and use Javelin class definitions

Summary:
Ref T4324. The server code is probably going to get a fair amount more complicated, so allow it to load Javelin classes in a mostly-reasonable way.

This integration has a few warts, but should be good enough to let us manage complexity through the next iteration of the server.

(Mostly I just want the concicse Javelin mechanism for defining new classes.)

Version bump is just so I can figure stuff out if this creates any issues for users based on which version of things they're running.

Test Plan: Started server, posted some messages through it.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4324

Differential Revision: https://secure.phabricator.com/D8253