Fixed categories and generic comment, added german translation
Perhaps add info about this in https://github.com/micahflee/onionshare/wiki/Translating so translators can know they need to translate this file also. Or even better add the strings to the .json translations files so alle strings are in one place.
- Remove UTF-8 entry - it is now redundant; see http://standards.freedesktop.org/desktop-entry-spec/latest/apc.html - Add some suggested keywords; see http://standards.freedesktop.org/desktop-entry-spec/latest/ar01s05.html
