Separate width and height parameters for Image widgets

Fix analyzer warnings

This change makes it easier to defined only the width or the height of an image
and let the other value be filled in from the image's intrinsic aspect ratio.

Fixes #175

Renamed AnimatedType to AnimatedValue

Updates sprite widget to handle changes to renderbox

Dismissable: animate "snap back", only call dismiss() once

Try to clarify initial execution.

This function took innerConstraints as an argument but used constraints internally.

Measurement tracking for fitness app.

There is an issue with the input control that prevents actually creating a measurement. Working on this with eseidel.

R=eseidel

Card Collection dismiss animation

Tweaks to launcher

Conflicts:
	sky/sdk/lib/rendering/flex.dart

Support for non-alphabetic baselines

Also, stop pushing the SDK to sky_sdk now that this repo exists.