Sending command 'client_kill' on stop button click now.

Killing a container only if command client_kill was send.
Moved propmpt to prompt.js

app/assets/javascripts/editor/execution.js.erb

@@ -39,10 +39,11 @@ CodeOceanEditorWebsocket = {
   },
 
   handleExitCommand: function() {
-    this.killWebsocketAndContainer();
+    this.killWebsocket();
     this.handleQaApiOutput();
     this.handleStderrOutputForFlowr();
     this.augmentStacktraceInOutput();
     this.cleanUpTurtle();
+    this.cleanUpUI();
   }
 };