Update generator-aura to latest Aura boilerplate

This PR addresses #10. There is bunch of changes that you can see in commit messages.
Thanks for your commits @fudanchii. (#12 #13)

@addyosmani @dotCypress Give it a spin and merge if you like it.

TODO: 
* I haven't touched the Gruntfile.js template yet since it's still unclear what boilerplate's Gruntfile.js should look like. (See [aurajs/boilerplate/14](https://github.com/aurajs/boilerplate/issues/14)). Addy can you shed some light on this?
* When time permits I'll update default yo aura app look and feel ("Cheerio welcome..." that yeoman webapp-generator currently has) - low priority
* Figure out why aura:styles is being called if you try to re-create extension/component with same name twice.

Questions: 
* Boilerplate's license is MIT while generator-aura's is BSD... Any thoughts on this?
* Is there a way in yeoman-generator to pause execution while waiting for user input? (That's why I reorganized [aura:styles call](http://github.com/robertd/generator-aura/blob/master/app/index.js#L109) since command prompt looks really weird) 


Cheers