Move Cluster state information to its own class.
Merge branch 'sharding' of ssh://github.com/triAGENS/ArangoDB into sharding

Conflicts:
	arangod/Makefile.files
Next draft of ClusterComm API.

ClusterComm internals are unready and subject to change.
ClusterComm thread is not yet started and shut down.
ClusterState does not do anything (yet).