This is not a grand refactor yet, it's just cleaning up what we have
already, so that people who keep using this API (e.g. dialogs) have
something coherent to deal with.
The major changes are that Navigator and NavigatorState have the same
API now, that most of the examples use `<void>` instead of `<Null>`,
that the navigator observer can see replaces, and that the `settings`
is moved from ModalRoute to Route. I also cleaned up some of the API
documentation.
* replace child parameter with builder on showDialog
* change builder parameter to WidgetBuilder
* mark child as deprecated and expand documentation to cover this and how builder should be used
* tidy comments and address some feedback
* phrasing
* move space to prev line and add //ignore comments for deprecated member use
* address comments and fix it's its
* update code samples
* adds semicolon to code snippets
* Moved stuff around yet
* Fix depedencies
* Add more dartdoc comments to packages
* Remove Cupertino dependency on material
* Removed mountain_view package and added page transition test
* Fix analyze warnings
* Remove commented code
* Partial solution. Still need to stop the animation on the previous page for modal
* Some review notes
* Move the cupertino back gesture controller’s lifecycle management back to its parent
* Reviews
* Add background color
* Directional curves, full screen transition
* Don’t perform the exit animation if the incoming page is a dialog
* It works!
* Test structures
* Add a bunch of more tests and fix the gallery
* One more comment
* Review notes
* final controller
* Use that sweet sweet `is!` keyword
* Play golf, because I’m bitter that there’s no nullable `as` or something in dart
* Remove a space
* Review notes
* Remove the last deprecated test
* 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
