Added options to build.gradle to build a release apk. Also some gradle tweaks.
Added an overlay using a service that starts on App launch.

Google Play Services Speedometer now recieves updates faster.
Now having one speedometer handle all listeners in a smart way, dynamically connecting and disconnecting if listeners get added and removed.
Updated icon.

Icon is licensed under Public Domain and taken from: http://thenounproject.com/term/speedometer/36106/
Changes transparency of overlay.