Move settings processing down to C++ layer

[steveatinfincia]

The code that handles mapping the settings values and organizing them into models is currently in the QML layer. The code is pretty fast but by definition it's a loop of almost 100 items and it happens in the main thread, which on occasion causes hiccups in the UI. It's most noticeable when the settings window first opens and closes.

The settings maps and the associated processing code should be moved down to the C++ layer and run in a separate thread.