Update templates and example Xcode project files to indicate they've
been tested for Xcode 8.3 compatibility.

* Add platform_services sample

* update build.gradle to use latest scripts

* use FlutterActivity

* Updated ExampleInstrumentedTest.java and deleted FlutterPlugin.groovy

* Remove getRandom code from main.dart

* remove unused import

Required to support Flutter SDK paths with spaces.

This avoids Xcode complaining at us about unused xcconfig files (for the
time being).

As of Xcode 7, Apple recommends setting the bundle identifier in the
PRODUCT_BUNDLE_IDENTIFIER build variable and setting CFBundleIdentifier
to that variable in Info.plist.

As of Xcode 8, CLANG_WARN_INFINITE_RECURSION and CLANG_WARN_SUSPICIOUS_MOVE
are recommended settings.

* Update examples to lower the deployment target on iOS.

* Remove stray PRODUCT_BUNDLE_IDENTIFIER

This was erroneously added and overrides
the bundle for the gallery causing signing
to fail in my setup.

@chinmaygarde

* Remove PRODUCT_BUNDLE_IDENTIFIER from all Runner pbxproj's

This patch changes the default `flutter create` command to generate a
HelloServices-style app on iOS. As a consequence, the Atom integration now
fully works with HelloServices.

This file is now app.dylib.

Currently this service just returns mock data, but it exercises the plumbing.

This example shows how to build a basic app using a custom Xcode project.
Future patches will bring the functionality up to par with hello_android.