Previously, we used `Alignment`, which was difficult to understand. Now,
we just use an `Offset` scaled to the child's size, which is much easier
to understand.
* Add cupertino to gallery and add CupertinoButto
* Use single quotes
* Add disabled state
* Some review notes
* Make button animation more responsive and tweak timing
* Renamed things Cupertino
* Button with background, move cupertino demos, move material demos
* Move 2 level list too
* Refactor various demo route names
* Some review notes
* More reviews and add test
* Linter as
* Move private constant up
