Add skinning support for TapRing

[LumpBloom7]

As part of this, I've also made steps to resolving #740 by making sure that DrawableTap now reflect the proper bounding box.

• sentakki/hitobjects/tap/base

  • The mandatory base layer to the object.
  • Blendmode: Multiply
  • Will be coloured based on the standard colouring rules of hitobjects.

• sentakki/hitobjects/tap/glow

  • The shadow/glow layer
  • Blendmode: Mixture
  • Will be coloured black if the hitobject is not EX, and inherits the note colour if it is EX.
  • This component is 1.5x the size of the base layer, and is placed under the base layer

• sentakki/hitobjects/tap/overlay

  • An additional decoration layer that isn't affected by note colours
  • Blendmode: Normal
  • This component is exactly the same size as the base, and is applied on top of it

The skinned TapRing is also shown in the editor.