Major refactor. Apply http interceptors in the package. Add methods for managing tokens.

The tokenAuth factory has been removed and replaced with authenticationFactory
which now has 2 methods, login and logout.

tokenFactory has been added with 3 methods to get, set and clear tokens.

HTTP inteceptor has been moved to the package to set appropriate headers on
all HTTP requests.

No more boilerplate required in your app to use angular-token-auth.