[feature proposal] Easily activate prior /e/version on A/B devices

• /e/ version: any
• Device model(s):A/B devices

Summary

Assumption 1: On A/B devices, when updating the system, the previously current version of /e/ is kept in its partition and becomes inactive after finishing the update (as the updated version becomes active).

Assumption 2: In the "System updates" subfolder previously installed versions of /e/ are listed and can be manually deleted.

I propose to

• Limit the number of previously installed versions of /e/ to three and delete all older versions automatically. Like this the user can still keep an overview what versions he/she installed before, while assuring that the old versions do not block too much of the devices RAM space.
• enable the user to reactivate the old version that is being held in the inactive partition of the A/B device - in case of technical problems etc. (see muckup below)