Show all maps when selecting a mod instead of just maps from the mod

[Vegita2]

Keep in mind that some mods, especially from newer modders, replace vanilla maps with their own versions of them, without patches. This is also the case when vanilla terrain needs to be modified because there is not currently an easy way to patch tile data (as far as I know). So I think it would be best to have separate dropdowns in the map list. All vanilla maps would be under one dropdown, there would also be one for each loaded mod containing all maps from each mod. Unless you think having all the vanilla and modded maps in the same list would be ideal.

Originally posted by @XenonA7 in #278 (comment)