This reverts commit a79faace1b.
This change will be superseded in a non-breaking way by changing to static functions and deprecating GetInstance() entirely.
Improves consistency across all classes.
Affects Preferences, LiveWindow, and CameraServer.
Old commands Scheduler::GetInstance() was not updated as this is already
deprecated.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
