feat(gen): use grunt-bower-install for dep management

To sync up the generators, I added `grunt-bower-install` here. It definitely needs to be tested, and my computer is in a :poop:-y state for that. So, I thought I'd see if anyone here had a chance.

It turns out this isn't only nice for users, who will be able to inject dependencies automatically, but it's also created for some easier generator authoring. Less JS ifs, and more "let grunt-bower-install handle it." I attached a `spawnCommand('grunt', ['bower-install'])` callback after the scaffold finishes installing the NPM and Bower dependencies. Not sure if that's a good idea, best practice wise, but it works!