* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* add a CupertinoTab

* Add default background color

* Add a bunch of examples

* A bunch of tests

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* Add default background color

* review notes

* fix test

* review

* Rename CupertinoTab to CupertinoTabView

* remove final ; in sample code for analyzer