Separate thread for UI

[Nice3point]

Summary of the Pull Request

What is this about:

Support for a new thread for the user interface

Description:

The feature is added to the existing "Hardware acceleration" option. The new thread allows us to offload the main thread and reduce interface freezes while Revit performs its tasks.

Need more tests to add this feature and possibly change the code. Turning it off closes all instances of RevitLookup, which may come as a surprise

Quality Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[Nice3point]

The new thread probably gets around this issue https://github.com/jeremytammik/RevitLookup/issues/155 and situations where with a selected roof the UI slows down a lot, even in Revit itself.