Toggle Tilemap Layer Visibility

[cosmiccoincidence]

Summary

Add ability to toggle the visibility of tilemap layers on/off.

Goal

The ability is fundamental when working on lower layers like pipes and wires without deleting the above layers.

Make sure the ability only toggles visibility for the individual user and not others.

Visibility of all layers should immediately restore upon exiting the tilemap build menu.

(Maybe it would be better to toggle other layers to 5% transparency or to wireframes instead)