Remove Modules.override to allow other ServletModules to be installed in the injector

This is to resolve HubSpot/dropwizard-guice#8

Updated the GuiceBundle and JerseyContainerModule so that JerseyContainerModule no longer relies on Modules.override to swap the Dropwizard WebApplication for the standard Jersey one. Using Modules.override prevents other ServletModules from being installed in the DI container.

Using inheritance probably isn't the most elegant solution, but I've confirmed that it works, and the Dropwizard resource config is correctly being injected.

I've also confirmed that further ServletModules are correctly being added to the injector.