Refactor todo page

[libremente]

Is your feature request related to a problem? Please describe.

The to-do page should be refactored. Some of the repos should be unlisted, see also #571 for removing some filters.

Describe the solution you'd like

I'd like an easily browsable interface.

[libremente]

We should also consider creating a way to warn people of the fact that:

• some repos are unmaintained right now
• some repos use deprecated stacks or non-supported ones

I'm leaving this here for reference: https://www.gnu.org/server/takeaction.html#unmaint