Moved AcceptFriendRequest into UserInfoDialog.
Fixed crash in UserInfoDialog if an invalid response is received (friend id
is not contained in the response --> profile not found --> crash. Now
the friend id is stored in the request itself, and not needed in the response
from the server). Moved RejectFriendRequest into UserInfoDialog.
Merge branch 'master' of github.com:supertuxkart/stk-code