Clear Notifications

### Problem I have

Via Mastodon original Webapp, I can clear (delete) notifications: All or a selection of them.

I regularly use this feature to keep only those that interest me.

### Solution I'd like

I would like to be able to remove notifications in Phanpy: select some or all notifications in "Notifications" view and clear them.

Start by locating the Notifications view and tracing how notifications are displayed and refreshed. Check how the Mastodon client handles notification operations, then define completion as allowing users to select individual or all notifications and clear them from that view.

Written by the indexing model from the issue text.