Hidden and FadeIn mods don't work at all

[LumpBloom7]

A rather dumb oversight on my end.

In #86 I changed all of the animations from manual lerping in Update() to using drawable transforms in UpdateInitialTransforms(), but neglected to re-implement the Hidden and FadeIn mod behaviors.

On the bright side, this gives me the opportunity to rethink how Hidden and FadeIn would work :)

[LumpBloom7]

Due to the amount of unique note type behaviors (laned notes, Touch notes, TouchHold notes, and Slide notes), I don't see Hidden or FadeIn working in a consistent way that I can be happy with.

Closing this as a "won't fix".