Add Gradle support

* Change project structure.
* Change to use Gradle as build tool.
* Change to use Android Studio as the main development environment.
* Upgrade third party libraries.

The main parts of this migration has been done by @pertyjons, thank You.
Remove android-support library from the source.
Remove unused libraries.
Add ignore of tasks.xml
Update gradle to 0.7 and 1.9.
Remove ad related code.
Add Idea project files.
Fix idea project.