KTutorial 0.5.1 released!

KTutorial 0.5.1 changes:
-Relicense from GPLv3+ to GPLv2+ to be able to add the project in the KDE repositories.
-Add translations in several languages (thanks to the KDE localization teams! :) ).
-Fix not installing KTutorialCustomization.h header.
-Log whether QtDBus was found by CMake or not.
-Add debug area for KTutorial library.
-Several other minor fixes and code improvements.