ISPN-4357 Use a specific cache for managing protofiles

Also upgrade to protobuf-2.6.0 and protostream-2.0.0.Alpha3

Jira: https://issues.jboss.org/browse/ISPN-4357
        https://issues.jboss.org/browse/ISPN-4756
That will become a new jira. I've just discovered while updating some test it is not possible to update this cache via hot rod (which was the whole point of this PR). The fix should be easy: activate compat mode. That fixes all problems for hot-rod tests, but breaks server integration tests because remote-query-server/client modules seem to have new dependencies now, but they are missing from module.xml.