Relicence Funkwhale to AGPL

Following https://github.com/dansup/pixelfed/issues/143, I'd like to relicence Funkwhale to AGPL. The current licence is BSD-3, which is a really permissive licence (in fact, one of the most permissive), but is not closely aligned with the rest of the fediverse ecosystem. Read the previously mentioned thread for more insight about the pros of AGPL.

One of the issues with BSD or MIT licences is also that code could be incorporated into proprietary or commercial products, and that there is no incentive to contribute further modifications upstream. AGPL adress that.

If we chose to go on with this, we need explicit and individual agreement for every contributors. Do not hesitate to ask question and point out potential issues with AGPL we may have overlook. Nothing is decided yet, and you can give your input even if you did not contribute code to this project.

@hazmo @Jee @Bat @EorlBruder @tcit @Luclu7 @yelin let met know what you think about the relicensing (you can juste post "I agree with relicensing Funkwhale to AGPL" if you're okay with that and don't know what to say)

References:

• AGPL3 licence: https://www.gnu.org/licenses/agpl-3.0.html