Initial work of implementing differential sync.
Adding Netty snapshort repository.

Motivation:
Removes the need to build Netty locally. This will be remove when
Netty-5.0.0.Alpha2 is available in Maven central.
Adding XMPP diffsync
Initial client XMPP work
Client will send message in an explicit message param
Initial "it compiles" commit
Horrible hacking to get code working with Xmpp sync
Moving to aar packaging
Fixing message handling bugs
untangling google's registration id and diff syncs client id
Swallowing errors during broadcasting
Fixing errors serializing edits
Hacking on the client
Edits now always contain document info
Making senderid and api key configurable
removing commented code block
Initial addition of AeroGear.Sync
Initial attempt on integrating the XMPP server with the diffsync server.
Removing the restsync module.
Moved diffsync modules into the root module.