QtIFW

Add strict and relaxed parsing to Settings class.

* StrictParseMode -> creating binaries and repositories
* RelaxedParseMode -> running the installer/updater itself

Introduced parse modes to be able to use old settings (existing
ones on user systems) with new binaries. Add and adjust autotest.

Change-Id: I3f7c7357325661a1197400d8d8dc2a5ca8bed184
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>