Add SkeletonBox component

[Oksamies]

Current dependencies on/for this PR:

• master
  • PR #989
  • PR #990 👈
    • PR #991
    • PR #992
      • PR #993

This stack of pull requests is managed by Graphite.

[Oksamies]

Merge activity

• Jan 3, 9:16 AM: @Oksamies started a stack merge that includes this pull request via Graphite.
• Jan 3, 9:17 AM: @Oksamies merged this pull request with Graphite.