add a StreamID to the Pre/PostSource signals, and rename them to Pre/PostSourceEvent

 - modify the EventSourceProxy to pass the StreamID to the Pre/PostSource signals
 - rename the signals to Pre/PostSourceEvent (to be consistent with Pre/PostModuleEvent, etc.)
 - adapt all services to the change in the signals
Merge pull request #1575 from fwyzard/add_StreamContext_to_Pre_PostSource

Multithreading fixes -- Add a StreamContext to the Pre/PostSource signals