Update gegl.doap and AUTHORS

Make gegl.doap compliant to the new DOAP file style (GUADEC 2014):
* Add new mandatory fields 'description' and 'programming-language'.

Add bug tracker URL.
Update mailing list adress.
Remove trailing white spaces.
Add me to AUTHORS.
(cherry picked from commit 279b33eddb37c8d832b85252ec87e8920f26f852)