Gradle implementation

I enabled the project to use the Gradle build system which is now the recommended build system for Android.
http://tools.android.com/tech-docs/new-build-system/user-guide

Gradle will handle managing dependencies for us, for example instead of having to commit the android support jar, gradle will automatically pull it from a Maven repository and add it to the build path.

This will enable someone to import the project as a gradle project which will automatically download all dependencies and add them to the build path. This makes the setup less fragile than relying on everyone having the same eclipse project setup.

https://github.com/spring-projects/eclipse-integration-gradle/wiki/Gradle-Import-Wizard