Add abilty to clean-up inbox

[elishamint]

Is your proposal related to a problem?

As people get more active, it will be required to have ways of removing/deleting personal messages, and perhaps also reply and mention notifictions. We are not curently able to remove received messages from the inbox.

Describe the solution you'd like.

I can delete messages which I have sent myself but I suppose that would also delete them at the receiver's end.

We could have a delete button with each message which would permanently remove a single message (whether sent or received) from our own inbox, without affecting the receiver. Alternatively, there could be a check-box at every messages, and a button for deleting them in the page header. I'd prefer it this way because the selection could later on also be extended to other functionality.

If this is being implemented togeter with a filter-by-sender/receiver method, see #1239 , and a "select all" button, we would be able to delete whole conversations in one go.

I believe this would not require changes on the back-end.

Describe alternatives you've considered.

An alternative to permanent deletion would be a trash bin functionality as we are used to. This will likely require back-end changes, though, and might not really be required in Lemmy.

Additional context

#1239 "Add filter by sender/receiver name in inbox" is a related feature which should best be implemented together with this one.

Thanks very much!