Add support for Gradle and and Android Studio / IDEA 13

No code changes. Only moved files and added build config, more precisely:

* Source files now live in ``app/src/main/java/`` as per Maven conventions.
* Resources are in ``app/src/main/res/`` and assets in ``app/src/main/assets/``.
* ``AndroidManifest.xml`` moved to the ``app/`` module folder.
* Added SDK as module under ``sdk/``
* Added Gradle build files for the app and SDK module
* Removed installation instructions for Eclipse
* Bumped SDK API level to 10 since 9 isn't available anymore.

This has been tested with Android Studio 0.3.7 and IntelliJ IDEA 13.0.

I suppose since this is only project setup config, you won't need a signed CLA. If that's not the case, let me know in the comments, otherwise feel free to merge.