Refactor defaults to not have a hardcoded language

* Add default_language to GLSetting
* Add languages_enabled to GLSetting
* Reference GLSetting.error_reporting_* instead of using a hardcoded value
* Place the sample submission fields in settings.py
Major refactoring on multi language support in backend

* Use a smarter pattern for nesting values inside the lang code key
* Uniform the arguments that transact decorated functions take and pass a
  default argument to them
* Fix unittests to work with the new code
Remove unneeded imports
Remove reference to system_default_lang()
Comment out the stuff related to setting tip and submission expiration configuration
Set the key value to be the name of the field
Fix bug in creation of receivers
Fix bug in node serialization
Fix bug in submission creation.
Add method for logging exceptions
Outline algorithm for migrating form fields from OLD to NEW
localization fixes
updated DB to version 3 (fields translation supports) https://github.com/globaleaks/GlobaLeaks/issues/438
sanity check in l10 function
Merge remote-tracking branch 'origin/feature/backend-translations' of ssh://github.com/globaleaks/GLBackend into devel

Conflicts:
	globaleaks/__init__.py