Restructure java targets to be 1-1-1.

[jsirois]

Today there are many java BUILD targets that are subsets of a package. To maintain the BUILD files for these targets in a reasonable way, constant lists of source files are defined that can be subtracted out from target sources lists using the globs exclude facility. At some point pants will likely remove the ability to define constants in BUILD files and this mode of defining non 1-1-1 targets will be taken away, forcing duplication of file lists and the associated maintenance risk.

There are 2 complicating factors here:

1. re-packaging will likely break clients of the java jars - they'll need to fix imports; so, this will require a deprecation cycle
2. IIUC the official home for the java code is still inside Twitter walls; so, this refactoring really needs to occur in Twitter's repo and then be synced out here.