Create lists in collaboration

[foegra]

Killer feature that is missing for me: being able to collaborate on lists together wjtb another user.

[IRHM]

Hi @foegra, thanks for opening this issue! Hopefully we can get this done after #199 (and #553 is related).

I imagine we'll have to work on some way of inviting users to collaborate or requesting to collaborate on a list, so that you can't spam add everyone to your list if they don't want to join it.

[foegra]

In a similar way, like it's done in Moviemate application.