pygimp: fixes creation of GroupLayer objects

Calling gimp.GrouLayer(...) directly was broken -
(one could retrieve a layer group from the image
or use the pdb call to get it working)

Spotted by Markus Orreilly at
http://stackoverflow.com/questions/12608210/
Bug 725734 - Themes not alphabetized

qsort() the array returned by themes_list_themes().

(cherry picked from commit 2303ce910d206e9e6f95f1a35eb86fe7a16772f4)
Updated Latvian translation
Fixed Latvian