Reparse Configuration at startup asynchronous

Options loading is split into three parts:

• reparse configuration
• loading of non-compositing related options
• loading of composited related options not needing CompositingPrefs

At startup the reparsing of configuration is done through a Thread
to gain a little bit of less waiting.

Before something else accesses the KConfig for the first time we
wait for the thread to finish and perform the other two loading
operations of Options.

The settings depending on CompositingPrefs will only be invoked
if a compositor is going to be needed.

REVIEW: 104562