Problem/Motivation
When #3124762: Add 'lifecycle' key to .info.yml files is committed, we will have three new non-stable theme states. At present there is a visual affordance to experimental themes at admin/appearance. But nothing at present for obsolete and deprecated.
Proposed resolution
Promote the non-stable statuses in admin/appearance page, optionally even visually
Remaining tasks
User interface changes
Before unistalled themes
After unistalled themes
After installed deprectated theme as default
