fixes #2444 - locale selector in user account

Selector in the user new/edit page. Works for both admin and non-admin
users. By default it does show language country code (e.g. "es" for
Spanish), but once translators translate "locale_name" special string (it is
documented via TRANSLATORS comment) it does appear in the native name (e.g.
Čeština).

The default (empty) value is "Browser Locale" which detects automatically.

I am also fixing one line - in the new user action, Rails was giving Can't
mass-assign protected attributes: admin error - I took admin field out of
the mass assignment.