ISkinComponent
ISkinLookup
Of note, this removes the "major" barline triangles from legacy skins. I think this is more correct, as they did not display in stable.
Could cause overwriting of components added by base DrawableHitObjcet class (such as samples)
No reason for it to be a container.
Most issues were related to BeginLoopedSequence usage and lack of "this." in front of transform helpers.
Depends on https://github.com/ppy/osu-framework/pull/837