added discounts to memberships
fixes
merged with master, fix error for undeclared fields
Default discount_eligible to false.
Merge branch 'master' into 460_membership_discounts
Updated migrations, and added fixes
Merge branch 'master' into 460_membership_discounts
Updated discounts to membershipset instead of membershipdefault model
Added discount_amount and discount_code to invoice model
Merge branch 'refs/heads/460_membership_discounts'