Refactor device.dart

remove device type specific checks

'flutter apk' now supports dynamically registered services.

Third-party libraries can now provide their own mojo services. They do
so by adding a config.yaml file to their pub package which contains
- a list of service names and java classes which handles that service's
  registration.
- a list of pre-built .jar files to statically link with the app's shell
  when building the app.

Change Block children to be a named parameter

This is a backwards incompatible change.

Added TwoLevelList et al, a Material Expand/Collapse List Control

A TwoLevelList can can contain TwoLevelListItems, essentially ordinary list items, or TwoLevelSublists which have a list of items of their own. Tapping on a TwoLevelSublist causes it to expand, showing its items. Tapping again causes it to collapse.

Scroll focused input widgets into view

Add device pixel ratio to MediaQuery

When opening the keyboard or focusing an input widget, we should scroll the
widget into view so that the user can see what they're typing.

Don't autofocus Input widgets by default

Remove unused close method from AssetBundle

Instead, require the developer to opt-in to autofocusing because autofocusing
can be disruptive.

Fixes #1307

Scaffold should respect window.padding.bottom

The space for the keyboard is now represented as bottom padding for the window.
By teaching the scaffold to respect the bottom window padding, we move the
floating action button and snackbars out of the way of the keyboard.

This currently works on Android. I'll need to see how to get the keyboard
geometry on iOS for a similar effect.

Fixes #103

refactor commands to move out re-usable functionality

Move scroll_behavior into widgets

Previously this code was in the animation layer, which didn't make much
sense because scrolling is a widget concern.

parse out the ios simulator device name

Minor animation renames

These should be the last references to the old "performance" name.

Some of the Animation classes that we converted from performances use
the term "master" to refer to the animation upon which they're based.
This patch changes them to use the term "parent", which is consistent
with the rest of the animation classes.

Make `flutter start` not report erroneous failure

Was failing when starting in the iOS Simulator

@chinmaygarde

Merge simulationStepper into AnimationController

Now that we've decided that Animation<double> isn't confined to the interval
0.0 to 1.0, we can expand AnimationController to cover the use cases that used
to require SimulationStepper.

This patch merges SimulationStepper into AnimationController and ports the one
stand-alone client of simulation stepper over to using AnimationController.

Add section images to the gallery home page

Move ClampedSimulation into newton

refactor build command into two files

ClampedSimulation makes more sense at the newton layer because it's dealing
entirely with newton concepts.

Port the remainder of the framework to AnimationController

This patch removes Performance and AnimationValue now that we've ported the
framework over to AnimationController and Tween. This patch also cleans up the
names of the AnimationController classes now that they don't have to avoid
conflicts with the old animation API. Specifically, I've made the following
renames:

 * Animated -> Animation
 * Evaluatable -> Animatable
 * PerformanceStatus -> AnimationStatus

This patch is just renames and moving code around. There aren't any changes in
behavior.