CorePlugin: Compile with QT_NO_CAST_FROM_ASCII.

- Wrap literals in QLatin1String()/QLatin1Char().
- Extract some string constants avoiding repeated
  QString construction.
- Fix repeated invocation of Container.end() in loops.

Change-Id: If737735507aaf82e53063adda53f54c46418f42f
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>

src/plugins/coreplugin/actionmanager/actionmanager.cpp

@@ -311,7 +311,7 @@ ActionContainer *ActionManagerPrivate::createMenu(const Id &id)
         return it.value();
 
     QMenu *m = new QMenu(m_mainWnd);
-    m->setObjectName(id.name());
+    m->setObjectName(QLatin1String(id.name()));
 
     MenuActionContainer *mc = new MenuActionContainer(id);
     mc->setMenu(m);