DissolveUI error trying to destroy materials

[cfoulston]

DissolveUI access the material of a Graphic though "materialForRendering". This is just a pointer to a material, and could be an asset. Trying to destroy this results in an error:

"Destroying assets is not permitted to avoid data loss."

Maybe add the option to override this behaviour? Or let the user control the destruction of materials

[dimension5]

Fixed with #3 .