[Feature] - Maintenance Mode

[b1scuit-thi3f]

Is your feature request related to a problem? Please describe.
Currently, when deploying new plugins or updating jimi, users will notice disruption if they are actively using the system - for example in debug.

Describe the solution you'd like
Following on from #296, jimi would benefit from maintenance mode where debug sessions could be temporarily stored and users are warned of an incoming restart. This would reduce any disruption caused to users when performing updates, avoiding having to schedule updates/non-store plugin installs outside of working hours etc.