RestingScreen idle override should be registered to the Skill that called it

[krisgesling]

Is your feature request related to a problem? Please describe.
Overriding the idle screen from a Skill doesn't track which Skill created the override. Hence it would be possible for multiple Skills to be acting on the RestingScreen and interfering with each other.

Example:

1. Skill A is triggered, performing some action
2. Skill B is triggered and overrides idle
3. Skill A finishes and clears it's namespace
4. Skill B's idle override gets unintentionally cancelled by Skill A releasing the override

Describe the solution you'd like
Skills should only be able to perform actions on their own idle screen.
Need to look at how we handle multiple Skills wanting to be the idle screen. Currently a new one overrides an older one. Should it be a stack where Skills can clear their item in the stack, but if they haven't clearing all above would return to that?

Additional context
Arose from this discussion.