Add fees and discount on Cart

Remove CartStorage
Update JSON import / export
Add Rbs_Order_CreditNote document
Some fixes on admin interface (breadcrumb, context, editor, filter)
update admin routes
Rename Rbs_Price_Fee document to Rbs_Commerce_Fee
Add Rbs_Discount module in ECom package
Fix Rbs_Commerce setup. (remove \Rbs\Commerce\Events\CartManager\Listeners)
add CreditNote skeleton admin editor
Merge pull request #861 from inthause/documents

New Rbs_Discount module and  cart updates
Merge pull request #863 from loiccouturier/master

Enhance Product and Cart and add variant prices editor