Add lightmap baking

[nasOS-official]

Related to #15.

Please add support for baking lightmaps or add a "Convert to mesh" button.

[Calinou]

Duplicate of #15 and #95.

Note that exporting to the Godot mesh format has been implemented as of 1.0.2, so you can do that then bake lightmaps afterwards. Converting to mesh is a destructive operation, so you'll want to keep a copy of your source CyclopsBlocks around.