Doc: Fix references to Qt Test

QtTestLib and QTestLib don't exist. The proper name is "QtTest" (code)
or "Qt Test" (English)

http://qt-project.org/wiki/Spelling_Module_Names_in_Qt_Documentation
http://lists.qt-project.org/pipermail/interest/2012-December/005221.html



Files paths in qttestlib.qdocconf can't be changed easily however, as it
breaks things. So, they're left as they are.

Change-Id: Ifbc44ea858c453bedad8cd7723f847e67fc7a85a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>