Project class: add method to manage locale exception, update Gaia locales

* Move code from Bugzilla to manage exceptions in a single place in the code
* Clean up some views:
  * accesskey: use ```getRepositoryLocales```, no need for Gaia hack (no accesskeys in Gaia).
  * checkvariables: use ```getLocaleInContext```.
  * gaia: remove Serbian hack, tweak ```l10n-init.php``` to return the list of locales for Gaia in $all_locales.
* Update Gaia locales (master, 1.4): en-GB, fa, mr, nb-NO, sw.
* Fix markup error in changelog.