[Feature Request] Resource reference field

[Gamer-XP]

There are sometiems cases where you want to reference resource of a specific type. For example, you got an object that spawns an enemy - you need to specify type of the enemy that should be spawned. Or there may be an entity that does something with tiles - you may need to select layer it targets.

At current point. this can be done either with string or enum field, but that lacks automation and not very convenient to use.

Options for that field are:

1. What kind of resource can be selected: Entities, Levels, Tilesets, Layers. May allow multiple types of resources too.
2. Filter for given resources by tag. For resources that support tags only.
3. Filter for given layer by type. For layers only.