Added more logging to engine connection

Should make it easier to debug future issues. CURA-1133

plugins/CuraEngineBackend/CuraEngineBackend.py

@@ -163,6 +163,7 @@ class CuraEngineBackend(Backend):
                 self._process = None
             except: # terminating a process that is already terminating causes an exception, silently ignore this.
                 pass
+            Logger.log("d", "Engine process is killed")
 
     def _onStartSliceCompleted(self, job):
         if job.getError() or job.getResult() != True:

plugins/CuraEngineBackend/StartSliceJob.py

@@ -105,7 +105,7 @@ class StartSliceJob(Job):
 
         Logger.log("d", "Sending data to engine for slicing.")
         self._socket.sendMessage(slice_message)
-
+        Logger.log("d", "Sending data to engine is completed")
         self.setResult(True)
 
     def _expandGcodeTokens(self, key, value, settings):