* Let android create template have an explicit flutter splash screen flag

* minor language tweak

* Add iOS template

* Android

* Let the engine reset the theme without the activity knowing

* Small tweak

* Replace assets with different vectors

* Let the template hookup have no actual image assets

* Add back placeholder assets with 1px transparent pngs

* Fix drawable xml

* clean up an extraneous line in the storyboard xml

Added a PluginRegistry to the new project template. The registry files will be automatically updated at build time to register the native plugins.

Fixes #7814.

This yak shave went as follows:

Fix https://github.com/flutter/flutter/issues/8795 by adding stocks to
the examples README.

Notice the layers entry in that README isn't quite right either.
Update that.

Check the layers/README file is worth pointing at.

Update the layers/README.

Let's run some of the layer tests to see if they still work.

Oops, need to update them to gradle.

Ok let's try running them again.

Oops, sector is broken.

Add a test for sector.

Fix sector. Find you need to add an assert to a const constructor.

Notice we need to turn const asserts on for the analyzer.

Notice the analysis_options files are out of sync with each other and
with the full list of lints.

Turn on the lints that should be on.

Fix the bugs that finds.

Plugin projects are created by running `flutter create --plugin <name>`.

An example app is also created in the plugin project, using the normal 'create' template, which has been modified to allow for conditional plugin code.

Modified the android package name to match package naming conventions (all lower-case, and must match the directory name).

* Make new project template gradle-based for Android.

With this change, the 'new project' template uses the same gradle-based build for Android as the hello_services example. This has some implications on build performance, since we're now building a complete Android app instead of just combining a pre-compiled .dex with the Flutter assets.

The very first build is a little over 2x slower, since it needs to download gradle and build the build scripts before getting to the actual code. Subsequent builds with changes to the code are comparable to the old builds. Null builds are faster. Enabling the gradle daemon speeds up subsequent builds by around 5s.

* Move Flutter Gradle plugin to Flutter root.