Refactors the sprite matrix handling to do most calculations in Dart, minimizes the number of calls down to Skia

Refactors matrix handling in sprites

This file was deleted.

Avoid crashing when building an app without an app.skyx file in DEBUG mode.

app.skyx file in DEBUG mode.

Fix failing test card_collection.dart

Add a widgets.dart uber library

Now you can import 'package:sky/widgets.dart' to get all the widgets.

Rename some animation classes.

* Intentions => Behaviors
* SlideIn => SlideTransition
* FadeIn => FadeTransition
* removed unused AnimatedContainer intentions

Use transitions for Dismissable

Use SkImage instead of SkBitmap

Fix visual bugs in Stocks

Apparently SkImage is the new hotness.

Simplifies the code a bit.

Add support for FontStyle.italics

 - Center the labels on the tabs
 - Make the drawer's mask visible

Allow iOS apps to restart by copying the app.skyx to the Documents directory on the device.

directory on the device.

This work is to support a workflow where developers testing on an iOS
device will automatically see their app updates as they change their Sky
code. Currently this works by using the ios-deploy tool:
$ ios-deploy --bundle_id 'org.domokit.sky.game' --upload out/ios_Debug/game_app.app/app.skyx --to Documents/app.skyx
Upcoming commits will incorporate this into skytool.

Fix skyanalyzer

ScrollableBlock should be able to overscroll

Our supressions for the generated mojom.dart files weren't working after we
deleted the mojom package. This CL updates the filters to catch mojom.dart
files again.

When a ScrollableBlock can scroll, we want to be able to drag into the
overscroll region. Previously we could fling into the overscroll region, but we
couldn't actually drag there.

Remove sky:init

Now that we don't have a magicaly mojom package, we don't need sky:init.

Support borders with borderRadius

Add transitions.dart for common animation transitions.

Use those in SnackBar, Drawer, navigator instead of AnimatedContainer's
intentions.