Infoj Entry Type Key > Toggleable Layer Button

[simon-leech]

The infoj entry of type key exists in nearly every infoj.
It currently has no purpose except a label.
It would be nice for this to become a button that when clicked toggles display of the entry.location.layer.

This would become a button that was orange (active colour) when the layer is on, and grey (disabled colour) when the layer is off.

This is a little UI change to enable users to turn off the overall layer much easier.