* when dir system/cache is not writable by the webserver, then show some
nice notice to the user about it instead of http 500 error
* remember client version and usage stats checkbox in session on install
* fixed some small warning introducted yesterday about
highscores_ids_hidden
* updated TODO
* added anonymous usage statistics reporting
* (fix) don't show templates that doesn't exist in Menus option in Admin Panel
* (fix) menu ordering by category
* (fix) showing changelog with urls in Admin Panel
* (internal) moved uninstall logic to Plugins class