Fix Renderer and GPU threads on windows

These threads are using the UI message loop on Windows per default. This
won't work since the UI message loop is handled by Qt and the Renderer
and GPU threads won't work with it properly.
Force these threads for using the default message loop as they use it on
Linux platform.

Change-Id: Ie3582583e5d1644faa2875e015a0908ba148d91f
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>