* Fix focus switching when changing tabs in CupertinoTabScaffold

* review

* Test focuses are saved within tabs

* review

This allows the scheduler library to depend on the services library
and the painting library to depend on the scheduler library without
the services library having to depend on the scheduler library.

While I was at it I also cleaned up some of the binding logic: the
licenses logic can now be overridden (and the test library does so),
and the image cache can now be overridden as well.

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* Add default background color

* review notes

* fix test

* Things lay out but the effects not right yet

* Remaining functionalities and tests

* one line large title only

* Add more docs

* review

* started copying stuff into cupertino page route

* extracted from material page route. Ready for testing

* works with button and gesture

* tests and docs

* review notes

* review notes

* works using pageview
it’s a bit heavy and scrolls
no documentation or test yet

* docs and tests

* more docs tweak

* revert drive by page view changes

* swap out the indexed stack for a custom thing

* layout everything on the cheap
tests pass

* add more tests

* move back to stack and add docs

* review notes

* build all the tabs once built