Don't upload things again in stage two

Bump versions of sky packages

Add a --stage-two to big_red_button.py

Bump Dart runtime dependency

Stacked does not repaint when its position changes

Do not invoke mojom/generate.dart from sky_tool anymore

Bump sky package version requirements

We were marking the parent *Widget's* render object as needing layout, but
we actually need to walk up the component tree until we find the parent
*RenderObjectWrapper* so we can mark actually mark the parent render object as
needing layout.

Fixes #408

Make it possible to pass a URL via command line to Mac SkyShell.app

@chinmaygarde

Add --enable-checked-mode to sky_shell

Simplify Navigator's Transition code a bit.

Fixes anchor points for particles in particle systems

We need a way for developers to use release builds in checked mode.

Progress on #400

Fix loading SkyX files on Mac

Allow loading SkyX files on Mac desktop

Make Switch a standalone class with a custom RenderObject

Lower sky package requirements

This changes Switch from being a subclass of the Toggleable widget to
being a standalone Component with a custom RenderObject. This is to
enable adding Switch-specific radial reaction animations in a
subsequent patch. The CustomPaint logic that Toggleable was using does
not provide a nice way for a class and its subclass to both participate
in deciding to repaint.

Combine all the scrollable classes into scrollable.dart

The new output seems correct.

We ended up with a bunch of different scrollable widgets and it was confusing.
This CL moves them all into one library to make them easier to find.

Bump versions

Fix Dart analyzer warnings

Make fonts not awful on iOS