Update wrangler package for GTID refactor.
Update vt/worker for GTID refactor.
Add synchronized GetLastGTID() method.
Update vt/tabletmanager for GTID refactor.
Update vt/tabletserver for GTID refactor.
Update vttablet status for GTID refactor.
Move GTID flavors to proto package.
Fix inconsistent GTID encoding.
Update test/update_stream.py for GTID refactor.
Don't export raw GTID fields protected by mutexes.
Fix GTID encoding/decoding.
GTIDField no longer implements GTID interface.
Update integration tests for GTID refactor.