Tf2 republisher service

Change TFClient to use the new version of tf2_web_republisher (see RobotWebTools/tf2_web_republisher#15 and RobotWebTools/tf2_web_republisher#16 )

Travis job will fail until the new tf2_web_republisher is propagated to the apt sources. Sorry about that.
Want to also add a test in `test/examples`?