Add CheckedPopupMenuitem, update the Stocks demo

Simplify demo template

We don't need these keys. Also, improve style in several places.

Fixes #2225

some performance optimizations for starting apps

Handle conflicting 'library' identifiers

Move update_packages.dart to `flutter update-packages`

Update engine revision to pick up the fixes for instability on iOS

Also, handle the new directory structure of the flutter repo.

add timing info for flx creation

SizeObserver crusade: RawInputLine

decouple `flutter drive` from `flutter start`; make things in `flutter_tools` more testable

flutter start's method of finding devices to run the app on is not suitable for flutter drive.

This commit also refactors several tool services to allow mocking in unit tests.

Pin analyzer package so that we're consistent

Gallery Menu Demo etc

Now that we don't require the Dart SDK to be in your path, it's hard to run
./dev/update_packages.dart. Instead, you can now run `flutter update-packages`.

Fixes #1906

See the comment in the patch for details.

SizeObserver crusade: Dismissable

Update engine revision

Remove examples/fitness

We originally wrote examples/fitness to be an app which all
members of the Flutter team could carry on their phones and
use every day.  It served us well for testing of Text input,
Keyboards and writing/reading JSON.  It's never actually become
a real carry app, so lets just let it go for now.

@abarth @collinjackson

Ignore `flutter analyze` errors via analysis options.

Refactor Dismissable to not need a SizeObserver and to generally tighten
up the code a bit.

# Conflicts:
#	packages/flutter_tools/lib/src/commands/analyze.dart

Migrates error suppression from regexps to analysis options.
* Ignore TODOs.
* Ignore strong mode field and method overrides (see `InvalidFieldOverride` and `InvalidMethodOverride` in `strong/info.dart`.
* Remove stale regexp to capture refs to dead `dart:ui_internals` URI.
* Remove stale regexp to capture dead strong mode "will need runtime check to cast to type" error (https://github.com/dart-lang/sdk/issues/24542).

5 regexp downs, another small handful (~4) to go! :)

Do not create a font manifest if the app has no flutter.yaml

Migrates error suppression from regexps to analysis options.
* Ignore TODOs.
* Ignore strong mode field and method overrides (see `InvalidFieldOverride` and `InvalidMethodOverride` in `strong/info.dart`.
* Remove stale regexp to capture refs to dead `dart:ui_internals` URI.
* Remove stale regexp to capture dead strong mode "will need runtime check to cast to type" error (https://github.com/dart-lang/sdk/issues/24542).

5 regexp downs, another small handful (~4) to go! :)

Pulls in the following changed required for iOS:
* Application identifiers are legal UTIs.
* Dart precompiled dylib is not a candidate for dead code stripping.
* Account for relative paths on readlink in SnapshotterInvoke

Re-run `flutter create` on examples to fill in icons and other assets

Use pointycastle as crypto library. cipher is deprecated.