Improved layout of login screen.
Go back to main menu when login out.
Disable online/login widget while login/logout are in progress (to
avoid race conditions, i.e. a new login arriving at server before
previous logout was processed).
Added missing calls to Screen::init().
Added missing initialisation, some cosmetic changes.
Moved hash function from StringUtils into player, there is no
other use of that function.
Re-enable voting for addons.
Merge branch 'master' of github.com:supertuxkart/stk-code