Different means of expression for the 8 byte item structure's FreeParam
Will be expanding the ItemEditor so that it has a checkmark to toggle Extension Item editing behavior.
Removes IHeldItem as there's no need to abstract it.
Extracts logic from the building & terrain & field item editors for reuse / separation of concerns
Have FieldItemEditor select between Items & Terrain so that you can change the popup menu mode (view set delete)
Not sure how I want to show the terrain names...
