allow inheritance of @UseModules

This pull request allows the @UseModules annotation to be used on base classes. 

This would be very useful in the following scenario, which I come across often:
You have 10 different repository classes, and one test class for each repository. You want all test classes to extend RepositoryTestBase because they all need some standard dependency setup, and you want to use the @UseModules annotation on RepositoryTestBase to install a few Guice modules.

I updated JukitoRunner so that it checks for the @UseModules annotation on all super classes and merges the modules into a set. I also updated UseModulesTest to extend a base class to show that this works.