initial commit of couponing system. for early preview
improved: merchandising screen
improved: coupons processing
updated: ACL check for merchandising plugin
updated: filterCallback
implemented: added coupons tab to product edit screen
updated: bug fixed and improvements
update: small fixes
fixed: view assertion
update: wording for coupon system
updated: UI adjustment
updated: coupon UI improvements
fixed: return link on coupon widget
Merge branch 'develop' into feature/coupons

Conflicts:
	system/app/Tools/ShoppingCart.php
fixed: non combinable coupons apply
Merge branch 'develop' into feature/coupons

Conflicts:
	system/app/Tools/Tax/Tax.php
Merge branch 'develop' into feature/coupons
added: coupon uniqueness check
Merge branch 'develop' into feature/coupons
updated: coupons UI & styles