java/syncbase: Expose more ways to Watch

AddWatchChangeHandlerOptions now has a builder, though it might
be somewhat verbose to use.

Watch can now use these filters:
- specific collection
- specific row
- collection prefix
- row prefix

Tests added for some of them (not exhaustive)

Change-Id: Ib823421932cc6c26c999a93a33865bbf95a0380e
3 files changed