archive models in profile

When a user submitted a lot of models, their profile becomes quite cluttered. The `public` flag hides it from the public leaderboard, but leaves the private profile leaderboard cluttered.

Proposal: implement an `archive` function to hide models from users' profiles. I would still keep them in the database for the record and allow to `view archived models` in the profile to un-archive them (e.g. if archiving by accident).

(from #129)

Start by tracing how the existing `public` flag affects the profile leaderboard and how models are retained in the database. Define the archive and un-archive paths, including a profile option to view archived models; the work is done when archived models no longer clutter the normal profile view but remain recoverable.

Written by the indexing model from the issue text.