Major fixes:

- play_rhythm, fixed black background issue, this activity was not
  usable.

Minor:

- fixed confusion around translator context in geography
- fixed several typo in english
- memory*, more appropriate difficulty level
- Added new standard desktop file gcompris.appdata

Translation update:

- Updated Brazilian Portuguese translation by Rafael Ferreira
- Updated Czech translation by Marek Cernocky
- Updated Scottish Gaelic translation by GunChleoc
- Updated Greek translation by Yannis Kaskamanidis