Integrated with Coveralls code coverage reporter
Forgot to actually call the coveralls script
Ignored some files for code coverage and added README badge

The polyfills do not need to be tested and we have not implemented
testing yet for Simple Login, although that is coming sometime in the
future.
Moved polyfills.js to lib folder
Merge pull request #409 from firebase/jw-coveralls

Integrated with Coveralls code coverage reporter