* Add Colors.white38

* Update ThemeData.disabledColor and ButtonThemeData.disabledColor to Colors.white38

* Update pre-existing tests to expect Colors.white38 instead of Colors.white30

* Update API documentation to reflect these changes

* Implement ExpandIcon custom color, expandedColor, and disabledColor

* Update to use pumpAndSettle instead of hard-coded duration

* Update colors to unfocused state, added dark mode test to active state

* Fix Colors.white30 doc opacity value

* Add links to Material Design specifications to color, expandedColor and disabledColor

* Update API docs to reference dark theme material page

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

Fix the spelling errors in the dartdocs for the framework.

There are no functionality changes here, just documentation fixes.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* rotate expansion icon fully if initial state expanded = true

* add test case for initially expanded

* remove unused import

* Update expand_icon_test.dart

add linebreak

* import dart:math as math

I got tired of drive-by spelling fixes, so I figured I'd just take care of them all at once.

This only corrects errors in the dartdocs, not regular comments, and I skipped any sample code in the dartdocs. It doesn't touch any identifiers in the dartdocs either. No code changes, just comments.

Most of the framework widgets should work in terms of EdgeInsetsGeometry
rather than EdgeInsets so that their clients can supply directional
insets.

Moved everything icons related except the material icon button and the materialicon font list to widget

* more widget const constructors

* prefer const constructors

* address review comments

Rename State.config to State.widget
Rename State.didUpdateConfig to State.didUpdateWidget
Renamed all State subclasses' local variables named config to something else

Aggressively apply the const lint.

This requires all AnimationController objects to be given a
TickerProvider, a class that can create the Ticker.

It also provides some nice mixins for people who want to have their
State provide a TickerProvider. And a schedulerTickerProvider for those
cases where you just want to see your battery burn.

Also, we now enforce destruction order for elements.

Changed the ExpandIcon constructor to take a default expansion state.
If the widget gets rebuilt with a different expansion value, the
animation will trigger but the callback will not.

Added a widget that automaitcally rotates the expansion icon and
offers a callback interface that captures presses.