Make it fast to draw color icons

Instead of using a ColorFilter, plumb the information down to Icon and thereby
to Image.

...once the animation is done.

Dart supports this properly now.

Add a flag to TextPainter to use ParagraphBuilder

This patch makes it easier to experiment with work on ParagraphBuilder.

MaterialApp assumes that you're using material design.

Also move radial reaction and fix imports for stats box.

Split material design widgets out of widgets.dart

These are now part of material.dart.

Now that you import a top-level file for each layer of the Flutter
framework, within the framework we can use relative paths without being
worried about the copy/pasta problem we used to have.

Also, have dialog buttons use the accent colour.
Also, generally rationalise some of this stuff to match Material better.

Adds support for keeping track of contact points in physics

The root cause was that we crawled the tree to mark anyone who depended
on the updated theme dirty _after_ we crawled it to rebuild it. Thus, if
anyone was already marked dirty when the process started, then got
marked clean by the first (rebuild) walk, then got marked dirty again by
the notification, they'd be clean when they got the notification,
despite already being in the dirty list, which would cause an assertion.

Also IconTheme didn't have an operator==, so it was independently too
aggressive about updates.

Defunct DismissableState should not have live animations

Remove ButtonState

SnackBar throws exception on creation

Clients should just use a GestureDetector (or an InkWell) instead.

Added horizontal and vertical alignment properties to Stack so that the origin of non-positioned children can be specified. Currently all of the non-positioned children just end up with their top-left at 0,0. Now, for example, you can center the children by specifying verticalAlignment: 0.5, horizontalAlignment: 0.5.

Added IndexedStack which only paints the stack child specified by the index property. Since it's a Stack, it's as big as the biggest non-positioned child. This component will be essential for building mobile drop down menus.

Added a (likely temporary) example that demonstrates IndexedStack.

It was trying to grab the route's performance before it was created. Now we
create the performance eagerly again.

The Drawer should animate out when popped off the navigator

FlatButton highlights but doesn't tap around edge

Adds support for applying forces and impulses to sprite physics

Now we trigger the highlight from the InkWell so that it matches the tap.

Fixes #1525

Now with more clear ownership over the Performance.

Previously, RenderObjectElements didn't support being marked dirty. This
is fine, except for MixedViewport and HomogeneousViewport, which have
builder functions to which they hand themselves as a BuildContext. If
those builder functions call, e.g., Theme.of(), then when the theme
changes, the Inherited logic tries to tell the RenderObjectElement
object that its dependencies changed and that doesn't go down well.

This patch fixes this by making RenderObjectElement a BuildableElement,
and making MixedViewport and HomogeneousViewport hook into that to
rebuild themselves appropriately.

Also, this was only found at all because ThemeData didn't implement
operator==, so we were aggressively marking the entire tree dirty all
the time. That's fixed here too.

Also, I changed card_collection.dart to have more features to make this
easier to test. This found bugs #1524, #1522, #1528, #1529, #1530, #1531.

Separate Route and PerformanceRoute