Implement Lint check

Will scan Java files for instances where Log.x is used rather than Timber.x
and presents them as warnings.

There is a way to include the lint.jar inside an AAR which will make the build system automatically recognize it, but the process for this is still in development. Here is a thread details ing: https://groups.google.com/forum/#!msg/adt-dev/seWAK5r1fjI/pDF6uWs9ipoJ

This PR does not include any auto-detection. Rather, users will still need to move the generate lint jar into the appropriate directory on their system.