Don't crash if no widthFactor is set in an unbounded context

We throw an exception if you tap the screen during load

Inside runApp, we were building the render tree for the app, but we weren't
calling layout, which meant we were running a hit test on a dirty tree. Now
hitTest specifically asserts that the tree is clean and we synchronously call
layout for your app during runApp.

Fixes #1960

Heroes don't reverse any more

We need to use the performance for the "from" route when going backwards. Also,
fix a bug in the HeroParty where it would call the quest finished callback
multiple times.

Fixes #1958

Adds showBottomSheet(), AlignTransition

Remove scaffolding for Navigator1 to Navigator2 transition

Better asserts for MaterialApp and Navigator

These types belong at the MaterialApp level.

Fixes #1969

Teach Block about padding.

This patch paves the path for refactoring the Drawer into the Scaffold to
support edge swipes and peeks.

It's common to want a scrolling viewport but with padding around the
contents. Teaching Block about this makes the places that do this
substantially simpler and further buries ScrollableViewport and
BlockBody (they're now only used in scrollable.dart).

...and clean them up so it's easier to understand them.

Draggable is now itself a gesture arena member. This means it won't
conflict with other gesture recognisers in the same path.

This also allows variants of Draggable that are triggered by other
gestures.

Also, some cleanup of DoubleTapGestureRecognizer, GestureDetector, and
PrimaryPointerGestureRecognizer.

Also, make MultiTapGestureRecognizer support a timeout for longpress.

Also, make Draggable data be typed.

Also, hide warnings about constructor warnings for now. Analyzer doesn't
support them yet. (Have to do this on a per-line basis)

Directions for future research:
 - animating the avatar (enter/exit transitions)
 - interaction with the navigator (canceling a drag on page navigation, etc)
 - double-tap draggable

- runApp(new MaterialApp()) was crashing long after the constructor. Now
  it asserts in a more useful location.
- remove the default name for NamedRouteSettings. It was unused anyway.

Fix updater. It was looking for the wrong files.

A translucent gesture detector still listens for gestures but also lets the
content visually behind the detector receive events.

Now a RenderBox is considered hit if one of its children are hit or it itself
decides that it's hit. In particular, empty space inside a flex won't be hit
because none of the children are located there and a RenderFlex doesn't
consider itself hittable.

Fixes #53
Fixes #1221

One Scaffold layout to rule them all

Expanded the existing CustomMultiChildLayout to handle all of the Scaffold's children.

This change also eliminates the FAB input dead-zone.

Remove use of FakeAsync in signing_test.dart

Make all the *GestureRecognizer classes inherit from a class called
GestureRecognizer. Give the old GestureRecognizer a name that is more
precise about its purpose. Remove the members of GestureArenaMember that
aren't used by GestureArenas.

Fixes navigation back to main menu in demo game

Check platform before opening /dev/urandom

- change how we expose settings at the RenderObject layer so that it's
  easier to maintain.
- expose the Widget owner chain in the RenderObject layer debug output
- add debug info to RenderOpacity, RenderIgnorePointer, RenderListener
- make the output for text nodes prettier

This means we no longer depend on the dart 1.13 beta SDK.

Add a test for signing/verifying with a random generated key pair.