Adapt to spotify-make, various fixes

As previous request, rebased to current spotify-make. Notes:
- The use of spotify-make gives a cleaner spec IMHO
- The filtering is partly broken, see separate commit
- The use of the register.sh scripts doesn't really work when packaging - current installs
  stuff in scriptlets which becomes unowned by the package.
- The suse-update-desktop macro is resurrected from last pull request.