Correctly listen to group change events

[simonspa]

In order for group sharing to properly work, we also need to listen to changes in the group:

• A user is removed from the group (Group\UserRemovedEvent): We need to remove all pictures from this user from all albums unless they are shared also directly with the user
• A group is dropped completely (Group\GroupDeletedEvent): We need to remove the group as collaborator from all albums and remove all files added by users in this group unless they also have a direct share of the album

This MR builds on top of my other MRs and I'd be happy to rebase this branch once the others are merged.

[artonge]

• A user is removed from the group (Group\UserRemovedEvent): We need to remove all pictures from this user from all albums unless they are shared also directly with the user

• A group is dropped completely (Group\GroupDeletedEvent): We need to remove the group as collaborator from all albums and remove all files added by users in this group unless they also have a direct share of the album

I think that we should delete the photo even if the album owner has access to the photo through another mean. It makes things simpler and is probably what a user would expect.

[simonspa]

I think that we should delete the photo even if the album owner has access to the photo through another mean. It makes things simpler and is probably what a user would expect.

I would expect the opposite actually. Imagine:

I create an album "NC Photos Hackweek" and share it with you. You add your pictures to it. Then we decide to also share it with the rest of the NC Photos team as group share. Later we realize that that's not a good idea and remove the group share again. I would expect your pictures to stay in because you are still a shareholder (sorry, collaborator) of the album. Your pictures would have been removed only because you also happened to be in the NC Photos team.

[simonspa]

...to add: the issue is that we cannot determine by which means (group or direct share) a photo has been added. (and it's good because knowing this would make things even more complicated... 😄 )

[artonge]

I misunderstood your initial comment, I thought "unless they are shared also directly with the user" was referring to a classic file share.

Other PR seems bundled inside this one. I'll review the code of this one once the other are merged :).

[simonspa]

Ah, sorry, no - I stayed completely within the Photos realm. :) I agree that folding in other sharing types into this is neither sensible nor easily feasible.

I'll rebase this once the others are merged.

[simonspa]

@artonge rebased and ready for review! 🚀

[simonspa]

/backport to stable25