Implement support for TranslatableModel.Meta.ordering option. Fixes #12.
Merge pull request #185 from spectras/feature/ordering

Implement support for TranslatableModel.Meta.ordering option.
- supports shared and translated fields
- if using translated fields for the default ordering, remember to override it when using FallbackQueryset
Remove custom model metaclass and use Django builtin class_prepared signal instead.
Merge pull request #188 from spectras/feature/metaclass_removal

Replace custom metaclass with 'class_prepared' signal to prevent conflicts with other modules.
Implement TranslationQueryset.fallbacks for Django 1.6+.