Before this commit, the tabViewItems and the segments were 2 different
collections. Any indexed change in the tabViewItems asked to re-sync
the segments making it difficult to maintain any persistent state. Now
the tabView items are the segments content.
Also fixed the selection update when items are removed.
See CPTabViewTest.j and manual test Manual/CPTabViewNib/
- should not force empty space above and below, but only where the tabs are
- box should fill frame when no tabs are present
- ivars should be prefixed with underscore
- not sure about the current background color code, may revisit