[Qt-creator] Reset to kit settings for CMake configuration

[Toralf Lund]

While doing some tests involving switch between different kits, I 
somehow managed to get into a situation where the Build Settings page says

CMake configuration set by the kit was overridden in the project

I did not want that. How do I reset back to the kit settings?? There is 
no obvious way to "reapply the kit", and the "Reset" button is not 
active when I select individual settings.

- Toralf