A lot more nice improvements!

A lot more nice improvements!
- Extensions does no longer have $EXT_LANG_PREFIX which defaults now to the
  extension's name
- ADD_POINTS_REFSYSTEM() and SUB_POINTS() prepare for upcoming extension
  'booking' which gives the admin and users a list of all booked points
- In user admin profile (what=list_user&u_id=x) and with installed extension
  'country' the country will be displayed again
- Three dashes added below "lock reason" in user admin profile
- Direct registration link of extensions now no longer showed if the extension
  is already installed
- List of users w/o referal id (refid=0) are now handled by
  "what=list_user&mode=norefs" and is no longer available in member menu
- Page navigation and sorting for user list extended for above changes
- Same list again rewritten for list of confirmed/locked users.
  Confirmed/locked: what=list_user&status=confirmed/locked
- URL redirection extended with "a" tag
- Some minor fixes here and there...