MIDI config doesn't persist

[Ashoat]

When I initially wrote the code to store MIDI presets and config in SpectrumConfiguration, I knew that persisting them to XML would be an issue because I was using custom structs stored in collections.

1. To make sure that the custom structs could be persisted to XML, I used XmlInclude annotations when declaring them
2. The relationship between the MIDI config UI and SpectrumConfiguration is handled imperatively, and more than half of MainWindow.xaml.cs is dedicated to handling it
3. In a lot of cases I call this.SaveConfig() manually to make sure that the config gets persisted. However, when debugging this issue at the burn, I added more SaveConfig calls, and they didn’t seem to correctly persist changes to the collections

I am pretty sure that this stuff was working when I first built it, given how much specific work I seemed to do to try and get it working. But it clearly isn’t working now.