Added mechanism to vtkSMTimeKeeperProxy to suppress time reported by
resgitered time sources. vtkSMParaViewPipelineController handles
suppression of timesteps from filers that add time.

Remove pqPVNewSourceBehavior since it's no longer useful. Cleaned up
pqDeleteReaction to better handle proxy deletion. Removing
pqDeleteBehavior since its no longer applicable.

Change-Id: I7c6fe6bf04ed05c060b73ec49318e31820f56e0e