Few mods to SkinnableComponent.
- Get rid of invalidateFlags and add in boolean for skinStateIsDirty which is the only thing it was used for. Put the logic for this in commitProperties rather than in validateProperties()
- Make skinObject a public read-only property. _skinObject is a protected read-write version of it.
- Added some extra comments for some of the methods.
- Updated clearSkinParts to not only remove static parts but also dynamic parts.