Moved achievements data into PlayerProfile (and data is saved in players.xml
now instead of in a separate achievements.xml file).
Removed unnecessary save function.
Renamed AchievementsSlot to AchievementsStatus.
Merge branch 'master' of github.com:supertuxkart/stk-code
Fixed memory leak.
Some refactoring in he Achievement classes, code style cleanup.
Fixed missing initialisation of m_reset_after_race, and added
error message in case of missing achievement data.