[libcalamaresui] Notify step number when modules are all loaded

- using the QML sidebar would not highlight the first step on startup,
  only after next / prev would the highlight show up. Now, notify
  when all the modules are loaded (and number 0 is active).

src/libcalamaresui/ViewManager.cpp

@@ -252,6 +252,8 @@ ViewManager::onInitComplete()
     {
         m_steps.first()->onActivate();
     }
+
+    emit currentStepChanged();
 }
 
 void