Added an experimental Terrain mod item.

Added button "Import Loaded Map" to copy an existing map to a modded map. In order to use it, first the desired existing map has to be loaded and reloaded into the map editor.

Added button "Import Loaded Map" to copy an existing map to a modded map. In order to use it, first the desired existing map has to be loaded and reloaded into the map editor.

Reimplemented using custom mod items. Still compatible with old mods.

Region modding uses the built-in mod item, that was not working.

Added region modding