Update build to leverage Gradle subprojects

* Update to Gradle 1.12 (from 1.11).
* Within repo dependencies updated to reference other subprojects. Gradle will take care of figuring out the dependency chain. Side benefit of this change is that we can now call a subproject's tasks: `gradlew :Utilities:tasks`
* mv Utilities/AndroidUtilities/AndroidUtilities -> Utilities/AndroidUtilities and TDH/Android/Android -> TDH/Android

*Note*: globalBuild will be **broken** until the other repos (couchbase-lite-android and Tor_Onion_Proxy) are updated to support Gradle 1.12. Need to update gradle-plugin used by couchbase-lite-android and Tor_Onion_Proxy_Library/android.
Why did you change the minSdkVersion to 19? It was previously 18 and that was important because my test device is 18.