[Feature Request] Add method to new notes-loader to define difficulty scales.

[TheT113]

This feels like a simpler way to handle the issue than trying to come up with a way to convert ratings:

Simply allow the simfile to have the info about what type of difficulty it is, and then: show an icon next to the difficulty, for what type of difficulty scale it uses. IE, a DDR arrow for DDR, an X for X, and ITG arrow for ITG.

(naturally, also use this to take into account which simfiles should be in red).