Localize Property model
Use t helper for translations form labels

Also fix form buttons positioning on the forms where there's no side
menu
Add i18n configs to general settings admin UI
Add spree_i18n install generator
Set up a SpreeI18n::Locale class

To list only locales availble on the config/locales dir of this
extension instead of all locales available through
I18n.available_locales
Force dependencies versions
Merge branch 'translate_models' into develop