Made building the Cast Sample easier

by leveraging the CastCompanionLibrary published to our public maven repo and by using
ANDROID_HOME to find the Android SDK's extras m2repository directory
and resolve the play-services dependency.

BasicCastSampleApp/src/main/res/values/version.xml

  * Updated google_play_services_version.

build.gradle

  * Modified the repositories.

  * Modified the Cast dependencies.

settings.gradle

  * Removed googlecastDependenciesAreSatisfied() and it's use.