Fixup of sessions

- Move newSession to Server interface
- Cleanly handle disconnects and disposes
- Only interpolate render transforms in same world, else use live
- Only perform one copySnapshot per tick (Why was this doing the same code
  three times @Raphfrk ????)

Signed-off-by: Chris Sanders <zidane@outlook.com>
Merge branch 'session-fix'

Signed-off-by: Chris Sanders <zidane@outlook.com>

Conflicts:
	engine/src/main/java/org/spout/engine/SpoutClient.java