Select-all, deselect-all, toggle-all control settings for Resource layers in Terrain Overlay tab

There can be many cases where a player would like to reference the terrain grid while not in Place or Designate mode, and in which resource bars obscure their view.

Please consider implementing (or making more obvious to users if there is already) global visibility controls for the set of Resource layers in the Terrain Overlay tab, such as select-all, deselect-all, and/or toggle-all controls.