Correctly track and now actually report running/paused status

It's quirky, we have to pass the stopped event to LoadThreads so that it
can correctly work out the state of any _newly_ added threads. We now
also correctly apply the allThreadsStopped=False behaviour where you
must not allow expansion of such threads (in theory, that's untested).

python3/vimspector/debug_session.py

@@ -1136,6 +1136,7 @@ class DebugSession( object ):
     pass
 
   def OnEvent_continued( self, message ):
+    # FIXME: allThreadsContinued ?
     self._stackTraceView.OnContinued()
     self._codeView.SetCurrentFrame( None )