Map Palette/Select from Map

This would be a palette of the objects, wall types, flooring, etc. that are in the current map. When creating a map, it's common to want to maintain a theme and searching for "that wall" or "that fountain" can be annoying.

An alternate implementation would be "select from map" -- this works for objects (with +), but for multi-level structures, it is less useful. It would be handy for things like floors and walls, however.