Free the desktop up from the old kdeext player entries

It is not that simple commit as its short message may say. It involves the
refactoring of the following items:

* CMakeLists.txt
* desktop file move
* ui.rc file move
* CPack rule corrections
* Include guard corrections
* About data corrections
* Desktop file entry change to the new schema
* and so forth

Testing: It works properly on Linux by running the player as
"gluonplayer-desktop".