Use modelFor('currentOrder') to get voucher list.
Move DonationPreview to projects.js.
Small Ember model cleanups.
Remove donations from voucher orders and remove vouchers from donations.

BB-648
Catch exceptions from DocData when generating payment url.
Small cleanup of DonationSerializer.
Merge pull request #446 from benkonrath/order-voucher-payment-cleanup

Order voucher payment cleanup