Fixes #1863 (NetworkViewManager may cause NPE and deadlock when disposing session with many network views)

Change-Id: I1740616af0a5e473f9807337e8d8928847d4301e
Fixes #1752 and #1736 - The Session Writer can now be cancelled properly as well.

Change-Id: I163f783113814b7fbf37fc8c1520d3bb7716d589
Refs #1823: Fixed issue with initial default style not being loaded correctly because it's loaded as "default_0".

Change-Id: Id2a77b57a70709697b4ced720ed72735a2cc729e