Specific maps for Heart Gate

[YellowLink]

A useful feature I think would benefit users of this mod is being able to specify certain maps for the Heart Gate.
The way it currently works is you can only specify a Level Set to choose from.

Instead, I suggest adding a field to specify certain maps, akin to how you can for the Rainbow Berry entity.

This would be useful for certain projects as well as giving more freedom to people using this already incredibly useful mod.