-RM-389-MR-Empty/white dialog boxes when using WUIGridWidget

Problem: If you add a module with an opened WUIGridWidget all dialog boxes, e.g. save project or file picker, are empty/white, see attached image. If you have added the module, but no view was opended so far or the view is closed on start, the dialogs are ok, e.g. you can choose your file. The error does not occur in modules which are using a WUIViewWidget.

Reproduction: You can reproduce the bug with the Template UI module.

Open OpenWalnut

Add Template UI module

Open/Activate widgets/view of Template UI

Open Load dataset ... dialog

** expected: you can choose your folder/file ** present: dialog box is empty/white/gray or broken

Versions:

Ubuntu 12.04, Qt 5.3.2 (online installer), OpenWalnut rev. on default ~10.12.2014
Ubuntu 14.04, Qt 5.2.1 (repository), OpenWalnut rev. on default ~10.12.2014
XUbuntu 14.04, Qt 5.4.1 (online installer), OpenWalnut Release_1.4.0rc3
hg bisect tells me that the error appears first in:

Änderung:        7233:0c8b3691c00f
Zweig:           OpenWalnut_1.4
Vorgänger:       7227:ba62ab063160
Nutzer:          Sebastian Eichelbaum 
Datum:           Sat Oct 11 20:17:58 2014 +0200
Zusammenfassung: [FIX] graphics engine missed to alloc the viewer in 
single threaded mode, causing a crash on startup on MacOS.

(from redmine: created on 2015-03-13, closed on 2015-07-08)