Updates for Spree 2.2.x

- Fixed rails4 finder scope
- Add missing translation keys + add Swedish locale
- Updated assets paths
- Changed so GroupPrice :name is required
- Tweaked layout with better icons and removed inline error messages
because they break layout
- Add missing “Back to Products” button
- Use .add_routes
- Find product by slug in spec
- Add LICENSE and minor README changes
- Moved generator into “install” sub dir