Material compiling complaints

Material compiling should not be modal. And you should be able to cancel it.

I know sometimes it’s not modal, but more often than not these days it blocks the UI while compiling. But even when it doesn’t, half the time I want to make a change and start the compile over.

Please make this more friendly. And please make it so that updates to params don’t cause it to recompile. It used to be like this, now it takes 30 seconds to see a single parameter change in the material preview.