ISkinComponent
ISkinLookup
SkinnableDrawable
SkinSprite
SkinnableSprite
allowFallback
SkinnableXXX
It makes little sense to set these when using RelativeSizeAxes.Both
Removes reliance on string lookups and better defines elements for introduction into database
Allows correct handling now that beatmap skins are also a thing.
Tidy things up, move logic out of SampleInfo.