Implement an option to fill selection natively.

[JaylyDev]

The editor seems to use the scripting API to fill blocks. There is a possibility that performance might slow down (and leads to hang?) when it comes to filling large amount of chunks. Consider implement an option to fill a selection natively for better performance.

[dacowan]

We will be working to optimize large block operations from the API, but in the meantime you can still use the /fill command