build: Upgrade to gradle 2.1
Update build to newest versions of dependent libraries
Fix deprecation warnings resulting from dependency upgrades
osm-binary: Merge changes from v1.3.3 tag of OSM-binary project

Re-sync osmosis-osm-binary with v1.3.3 of OSM-binary project.  Note that
due to the Osmosis version removing all unnecessary files, the only file
impacted by this sync is the release notes.
osm-binary: Upgrade to protobuf 2.6.0

Upgrade dependency from 2.5.0 -> 2.6.0.
Re-generate bindings using the 2.6.0 compiler.
The 2.5.0 and 2.6.0 runtimes are incompatible so Osmosis will no longer
run using the 2.5.0 protobuf library.