QmlCppDebugger: Decouple states of engines

The main engine now follows mostly the state of the gdb engine,
only if a breakpoint is hit/while stepping the state of the qml
engine is used. This allows us to hit C++ breakpoints at any time
(also when the qml engine hasn't been able to connect yet), and
also fixes the invalid transition warnings.

Change-Id: If67a56fd28b098952be2606d0a46e04c27835f66
Reviewed-on: http://codereview.qt-project.org/5897
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

src/plugins/debugger/debuggerengine.cpp

@@ -1208,6 +1208,12 @@ void DebuggerEngine::quitDebugger()
     case InferiorRunOk:
         d->doInterruptInferior();
         break;
+    case EngineRunRequested:
+        notifyEngineRunFailed();
+        break;
+    case EngineRunFailed:
+    case DebuggerFinished:
+        break;
     default:
         // FIXME: We should disable the actions connected to that.
         notifyInferiorIll();