Changes

Summary

1. UITheme is ab abstract class, turn color setting as subclass (details)
2. Add some more abstract methods for color settings. (details)

Commit 284bbb4bf8098f9e134ca3f456fae810962e08eb by hilaire UITheme is ab abstract class, turn color setting as subclass responsability.
	src/Polymorph-Widgets/UITheme.class.st (diff)
Commit 76bc7d3a27b6733e32f4331f9257d9b8bd2b1893 by hilaire Add some more abstract methods for color settings.
	src/Polymorph-Widgets/UITheme.class.st (diff)