Bug 925787 - separate fallback locale for fhr mobile from fhr desktop

* have a new list of fallback just for mobile: settings.LANG_MOBILE_FALLBACK
* Create symlinks for the mobile folder only based on the above list instead of having a general fallback
Merge pull request #152 from pascalchevrel/Bug-925787_fhr_mobile_locales_fallback_support

Bug 925787 - separate fallback locale for fhr mobile from fhr desktop
Update the list of locales that need to fallback to en-US because they haven't finished/done the translation for fhr mobile
Merge pull request #153 from pascalchevrel/Bug-925787_fhr_mobile_locales_fallback_support

Update list of locales with a fallback for fhr mobile