Add Donation origin

[Yann-BUTSCHER-EIRL]

Context

The users need to be able to track from which event originated a donation.

Todo

• [x] create DonationOrigin class
• [x] add crud for DonationOrigin in the admin section
  • [x] List
  • [x] Create
  • [x] Edit
  • [x] Show
  • [x] Delete
• [x] create a relationship between DonationOrigin and Donation
• [x] add a selector for the donation origin in the donation form
• [x] show donation origin in donation show page