Draft: First hack to add favorite albums

This MR aims at adding the possibility to add favorite albums.

Notes:

• I need a mentor to guide me further, I don't know much about Django so I'm a bit lost
• I basically took the track favorite code and replaced "track" by "album" (and use a bit of common sense when I could)
• I got three # TODO: ... in this MR: it's about values/fields that I really don't know if/how I should change

Related issue: #492

This Merge Request includes:

• Tests
• A changelog fragment (cf https://docs.funkwhale.audio/contributing.html#changelog-management)