Desura compatibility

- create launch scripts for Desura
- that access local installation launch scripts
- clean up /usr/* launch scripts created during make install
recommend Cg-Toolkit as soft dependency for Fedora/SUSE

it is in the non-free / RPMfusion repositories
package .desktop files for map editor on Linux, too

move desura scripts into packaging sub-directory
remove bashisms for extended portability
Merge pull request #2813 from Mailaender/desura

Desura compatibilty