new activities:
* categorisation
* guesscount
* bargame
* bargame_2players
* checkers
* checkers_2players
misc:
* Polish lang dataset by Łukasz Wojniłowicz
* Swedish lang dataset by Stefan Asserhäll
* Ukrainian lang dataset by Yuri Chornoivan
* new icons
* updated graphics on several activities
* website translated in Belarusian, Catalan, Catalan (Valencia), Romanian, Portuguese and Ukrainian
* new mingw windows builds
todo:
* Update screenshots page with new activities.
* ~~Update images for: ~~
*- ~~categorisation (at least the icon)~~
*- ~~bargame, bargame_2players (everything?)~~