Possibility to "Archive" an app

[Dean151]

Hi!

This is not an issue, more like a feature request.

It would be tremendous to give the possibility of "Archiving" an app. Sometime, a project will not come up as we expect, and might be cancelled, or delayed. Therefore, the only option today to remove it from the main dashboard is to delete it.

I propose an "in-between" state, Archive, that would allow to put the project in a sleep state for the dashboards.

But maybe a dashboard "re-ordering and hiding" would work as well. Anyway, no rush, just raw ideas dropped on a Sunday morning.

Good luck!

### Tasks
- [ ] App Model: add soft deletion
- [ ] App API: Allow filtering by soft deleted
- [ ] App API: Allow "un-deleting" 
- [ ] Web: Allow app archiving and unarchiving