new activities:
* categorisation
* guesscount
* bargame
* bargame_2players
* checkers
* checkers_2players
misc:
* Polish lang dataset by Łukasz Wojniłowicz
* Swedish lang dataset by Stefan Asserhäll
* new icons
* website translated in Belarusian, Catalan, Catalan (Valencia), Portuguese and Ukrainian
todo:
* Update screenshots with new activities.
* Update images for:
*- categorisation (at least the icon)
*- bargame, bargame_2players (everything?)