Add ability to toggle between enabled and disabled projects in /admin

[mathjazz]

Changing settings for disabled projects doesn't happy often (almost never), so we should hide them from the default view on /admin.

This same UI pattern could be used as is already is une on the team dashboard to toggle between projects that are enabled and not enabled for the team:
https://pontoon.mozilla.org/sl/

The button text should probably be just "Disabled projects >".

[flodolo]

This same UI pattern could be used as the toggle between enabled and not enabled projects for the team on the team dashboard:

What does "enabled/disabled" mean at a team level? Opted-in or not? If that's the case, I don't see practical benefits in doing that (you would also need to differentiate between project that can be opted-in).

[mathjazz]

This is a reference to the existing UX pattern we can use here. Rephrased the sentence above.