[master] Better spec coverage + fixes

- [x] Fix so specs pass.
- [x] Add more specs now 95%+
- [x] Fix all locales and removed sub locales with duplicate translations (tested with i18n_spec). Note that `activerecord` should be reached from `en.activerecord` and not `en.spree.activerecord` most locales had this wrong.
- [x] Add Swedish locale.
- [x] Moved generator.rb to sub "install” dir because it didn’t init on `rails g spree_static_content:install`.
- [x] Fix assets paths.
- [x] Admin pages tab moved to Configuration due to it made top menu items collapse, new form layout same style as products for consistency.
- [x] Fixed hooks, styles etc to correspond to Spree 2.1+ way.