Initial release

@himedlooff Please review when you have a sec. It still needs some work but I think we have a solid foundation. It scaffolds an application similar in structure to [cfgov-refresh](https://github.com/cfpb/cfgov-refresh) and installs selected bower components. I'd like to publish it to npm sooner than later to reserve the `yo cf` namespace.

Still to do:
- Only add Grunt tasks to the gruntfile that are relevant to the components selected by the user.
- Finalize user prompts (currently we ask for things like the user's homepage, not sure if that's necessary).
- Other stuff.
Is there a way we can use that repo as a dependency? Because there's a decent chance it will change over time, and having to manually update it in the generator is a recipe for the generator going out of date.