add karma-coverage and coveralls grunt task

I hope you like it :)
If you want me to change anything just tell me.

## my turn
- [x] get karma-coverage working
- [x] hook up to coveralls
- [x] add coverage badge

## turn of @Semantic-Org 
- [ ] register at [coveralls.io](https://coveralls.io)
- [ ] change the badge url