ImGui Load/Save rework

[azeno]

Is your feature request related to a problem? Please describe.
It's currently quite hard to trigger the Load and Save layout nodes properly.

Describe the solution you'd like
The ImGui region should take the LoadSettings (or maybe it's just a string) as an input. Whenever those settings change it will load them before the frame begins (but still inside the ImGui context). By providing a Dispose moment inside the region (this should be a language feature btw.) it should be straight forward to save the current settings when the app shuts down.