Mark project as Android library.
Add instructions for using as a library project.

For more details, see:

http://android-developers.blogspot.com/2012/03/updated-sdk-tools-and-adt-revision-17.html
Update namespace URI in progress_wheel_activity layout.

This is required when being built as a library.
Update project to allow Ant build.

(Command used: "android update lib-project --path . --target android-19")
Merge pull request #13 from pjdelport/feature/fix-library-project

Enable usage as a library project.