Improve debugging aids for widgets, rendering.

Kill the sky_server on Mac in a way that works to avoid unexpected behavior when working with more than one app at once.

Remove the skyx package

This code is now part of sky_tools.

We need a short name more often than a tree dump, so toString() should
be the short name.

Make debugDumpRenderTree() a global like debugDumpApp(), for
consistency. It's hard to remember the
SkyBinding.instance.dumpRenderTree() incantation.

Fixes #1179.

Adds TexturedLine and animated EffectLine to sprites

We were not removing children if they were more recently synced than we
were. This makes no sense. We should remove all children unless they
were synced this very generation already (in which case they'll be
somewhere else in the tree by now).

We removed this value from the engine because it's not useful.

What's important about this code is that it's presenting services outside the
VM, not the particular technology used to present the services.

This patch is part of a sequence of patches towards fewer top-level libraries.
In this patch, the gesture libraries are combined into one gestures.dart
library.

Conflicts:
	examples/widgets/scale.dart

First pass at support for pinch gestures; panning issues (needs testing)

Conflicts:
	sky/packages/sky/lib/gestures/drag.dart

Conflicts:
	sky/packages/sky/lib/gestures/drag.dart

Factor out GlobalKeyWatcher

- Reorder the methods so they are closer to run order.
- Reindent the code to match style guide.

This also moves the logic that tracks what Widget is being watched into
GlobalKeyWatcher, and much simplifies Mimic based on this.

FlexAlignItems.stretch didn't stretch

Please use GestureDetector instead.

Move Drawer to GestureDetector

This fixes an issue in the stocks app in horizontal mode where you could both
scroll and drag the drawer at the same time.

RenderView has to be a singleton for sanity during tests, otherwise they
all end up in the dirty lists and we end up pumping all of them each frame.

AnimatedContainer isn't an AnimatedComponent.

Turns out it gets nothing out of inheriting from AnimatedComponent.

This widget has no client.

Clarify why we don't assert that ancestor != null.

Be more explicit about what's state in dismissable

Move _activeCardDragEndPoint near build() so it's more obvious that it
is part of the build state.

Make a couple of functions use setState() since they modify variables
that are used by build().

Add a more detailed comment to the empty setState() call, since those
are dubious in general and need explaining when they occur, lest people
start using them as magic incantations to Make Things Work.

Follow-up for #1140.

If a StatefulComponent marks itself dirty, gets rebuilt, then its parent
gets rebuilt, its parent will find that its child is from a newer
generation and hasn't changed. Previously, we considered two stateful
nodes to not be syncable even if they were the same; combined with the
way the "old" node looks like it's been put elsewhere (since it's
already been synced), we end up confused as to why the new node is
already mounted.

This fixes the problem by making the canSync logic consider two
identical nodes as syncable (since they are; syncChild() short-circuits
that case), and by changing syncChildren to consider identical nodes as
matches even if they are already synced.

This specifically improves the reporting of exceptions in syncChild(),
and makes the way we've been adding information to toStringName() less
ad-hoc and easier to extend.