Theming support for composite styles

[jng]

Add support for creating themes for composite styles.

Due to the increased complexity of composite styles, we theme as follows:

• For each color in theme ramp the first defined fill color in the composite style. This could be:
  • A FillColor property of a Path graphic
  • A default value for a Fill Color parameter (if FillColor property is a symbol parameter reference)
  • The override value for a Fill Color parameter (if defined)
• Whichever one we find, we replace that color at that same spot in a cloned copy with the current color in the theme ramp.
• Add this cloned copy to the composite style

[jng]

Fixed r7999