change user config page to huggle3.css
multiple changes around huggle.css

* honor user-config
* sanitize page title (replace Special:Mypage) similiar to hg2
* introduce user-config-hg3 as user config var to be used by hg3
* use huggle3.css as use config name to prevent clutter with parallel use of huggle 2
* trying to fetch old huggle.css as fallback if huggle3.css doesn't exist (but writing config to new location at exit)
cleaned

Replacing Special:Mypage doesn't really work since it's called Special:MyPage and since it's not case sensitive we need to match any possible combination that could be used