Rename hamster-time-tracker to hamster everywhere

Created by: GeraldJansen

Reduce confusion about hamster / hamster-time-tracker [/ hamster-applet] by renaming everything from hamster-time-tracker to simply hamster (#472 (closed)).

Renamed directories (including ~/.local/share/hamster), schemas, desktop files, icons, etc., etc..

(The only place "hamster-time-tracker" is left is in the comments of the translation *.po files.)