Fix pulldown button theming

Without this fix, the pulldown button style displays using the same right-hand side widget as the popup button. This fix creates a new set of bezel images specifically for the popup button.
Fixed: CPPopUpButtonTest using non-existent methods.

There's no `selectedTag` getter for CPPopUpButton (although there's such a binding but that's separate). Also don't call private API that no longer exists - use proper public API instead.
Merge branch 'aristo2-pulldown-themefix' of https://github.com/ahankinson/cappuccino into ahankinson-aristo2-pulldown-themefix
Refs #1734. Include pulldown buttons in pop up button manual test.

These pulldowns are bound the same way as their corresponding regular popups.