[libcalamaresui] Another allow-to-fall-back-to-eventloop

With 1 CPU, Calamares still spawns 9 threads or so: eventloop,
dbus loop, QML loop, ... many of those are invisible to the
application. Contention occurs on startup when the UI is constructed,
and we end up with the module manager creating widgets alongside,
or ahead of, the main window UI. This can result in deadlock:

 - in CalamaresApplication::initViewSteps
 - in QML imports

This is partly because the signal-slots connections get "deep":
from loadModules() we emit *modulesLoaded* which ends up showing
the main window in initViewSteps(). Avoid this with a QTimer:
drop back to the event loop and release whatever locks are held,
so the QML thread can get on with it already. Then the timer
goes off and the view steps are created.

src/libcalamaresui/modulesystem/ModuleManager.cpp

@@ -281,11 +281,13 @@ ModuleManager::loadModules()
     if ( !failedModules.isEmpty() )
     {
         ViewManager::instance()->onInitFailed( failedModules );
+        QTimer::singleShot( 10, [=]() {
             emit modulesFailed( failedModules );
+        } );
     }
     else
     {
-        emit modulesLoaded();
+        QTimer::singleShot( 10, this, &ModuleManager::modulesLoaded );
     }
 }