Add Karma support (with Jenkins in mind)

I've added in a few pieces to allow karma support in the generator, as well as a default config and grunt tasks.

The new grunt task is a bit messy but does the job ob adding to the dom_munger's appjs to create a single flat array of files for karma's config (I couldn't work out a cleaner way to do this).

I was also wondering whether this should be added to the prompts to make it all optional.

We use Jenkins to autobuild and by using karma we can export XML that jenkins can parse in order to decide whether the commit is healthy or not. It also allows the use of end to end testing, and I think the next thing I'll do will be to include protractor.

What do you think?