Add support for other Android related versions

[MichaelEvans]

It'd be great to be able to pull the Play Services gradle plugin version and Android gradle plugin version as well. Seems like they both might be on jcenter already - (https://bintray.com/android/android-tools/com.google.gms.google-services/view and https://bintray.com/android/android-tools/com.android.tools.build.gradle/view) so perhaps just adding support for that repository would be the way to go? (As referenced in #4)

And while not necessarily a dependency - might be useful to also list the latest build-tools version.

[broady]

Also accessible here: https://dl.google.com/dl/android/maven2/index.html