Created authentication service which can be used by the theme

@hippee-lee @tsanko I have created the Authentication Service. Right now, it has the basic functionality to authenticate the user, and I've tested it against my local storefront to make sure that it works Cross Domain. The changes that I made on the server side have not yet been deployed out to samplestore.
I have made the first change you suggested. 

The `$http()` already returns a promise, so there is no need to wrap it in another.