Updates for Spree 2.2.x

- [x] Fixed rails4 finder scope
- [x] Add missing translation keys + add Swedish locale
- [x] Updated assets paths
- [x] Changed so `Spree::GroupPrice` `:name` is required
- [x] Tweaked layout with better icons and removed inline error messages
because they break layout
- [x] Add missing “Back to Products” button
- [x] Use new `.add_routes`instead of `.draw`
- [x] Find product by slug in spec
- [x] Add LICENSE and minor README changes
- [x] Moved generator into “install” sub dir

Note: I add so it send permitted attributes to Variant from initializer hope that was correct way. 

@jdutil :penguin: ping!