Layout saving

[CircuitLord]

This is already mostly implemented, and is just a bit buggy and doesn't have proper UI. Pressing the icon of 4 squares on the bar will save your current layout, and it gets restored on relaunching the app.

All the code for it can be found in DPLayoutManger, it's pretty much code-complete for saving any amount of layouts to files, and then restoring them.

A proper UI needs to be implemented, I had one in progress but it's not quite ready (the [LayoutsPopup] GO in the scene). Just let me know on discord if you want to learn more about adding new overlays and stuff.