Added Maven for dependency management and Robolectric for unit testing

- Maven can be used to manage dependencies. It can also be used to run
  unit tests and build the application.
- Robolectric is a unit testing framework which wraps JUnit and makes
  unit testing for Android devices much more efficient.

Signed-off-by: Byron Sanchez <bfs5030@gmail.com>
Updated Ant files to support Maven builds and to run unit tests

The updated Ant files allows installation of Maven files and
dependencies, which are specified in build.xml. In addition, unit tests
can be run using Ant, and unit test reports will be generated in the
out/ directory.

Signed-off-by: Byron Sanchez <bfs5030@gmail.com>