Remove Location.idl and assoicated code

Remove Screen.idl and associated code

Remove the DOM-based custom layout machinery

Run the Dart analyzer on Travis

We now do layout without a DOM.

Scoped focus, so you can have a dialog with input controls and not lose your focus in the background

Scoped focus, so you can have a dialog with input controls and not lose your focus in the background.

This introduces a GlobalKey registry so that you can tell when a key
has gone away (so you can unfocus dead dialogs).

Also I added an assert that you're not calling setState() during a
build. It turns out that doing so means you have a bug, because since
you're dirty already (you're building), you won't get rebuilt.

The focus code itself is gnarly. It uses a Component and an internal
Inherited TagNode to manage the focus state, and does crazy things
like updating its state during build to pretend retroactively that it
was built with some other state, once someone asks for focus the first
time (i.e. the first time it's examined, so you can't tell that it was
in a different state before). It does this so that it can autofocus
controls which otherwise wouldn't be focused.

This moves all the focus management into Navigator and showDialog(),
so the complexity is all buried deep and not visible to apps,
hopefully.

To do something like two tabs that each have an Input widget that
needs to be focused when you switch panes, you'd need to have two
Focus objects, one in each tab, and you need to set their autofocus to
true (maybe that should be the default?).

Fix review feedback from previous checkin.

@abarth doesn't like Futures that explicitly point out they're type-unsafe. :-P

Fix the lerp the RIGHT way.

Fix the crash for buttons.

pushDialog(navigator, (navigator) => new Dialog(...)).then((result) => process(result));

Turns out there was a typo in lerpColor.

Fixes #277.

Move fitness dialog into its own class

Use the navigator to stack dialogs.

Fix test breakage

This removes the need to manually include the dialog builder in the main window's build() function.
It also removes the need to track if a dialog is visible.

Other changes:
- I made dialog.dart a bit more readable.
- I renamed transitionFinished to fullyOpaque since that's what actually matters.
- I made Routes track if they're opaque. Eventually this should probably be more configurable when creating the route.

Directions for Future Research:
- Use this for focus management somehow.
- The popup menu should use something like this.
- We should factor the following out into a showDialog() function that returns a future for the dialog's exit result:
    navigator.push(new DialogRoute(builder: (navigator, route) { ... }));
- Maybe navigator.pop() should take a value to return to that Future.

Examples as libraries

Make the Mac target deps look similar to iOS

Fixes Mac builds

Optimizations for Particle Systems

Create //sky/packages/workbench

Converted demo launcher example to library

Converted fitness example to library

Converted hello world example to library

Converted mine digger example to library

Converted stocks example to library

Conflicts:
	sky/sdk/example/game/lib/particle_system.dart

Use Skia's drawAtlas now that we've rolled to a newer Skia

Dismissable animation simplifications; added backgrounds to CardCollection cards