Add local storage option for remember me

I'm writing a PhoneGap app. All the devices I support will have local storage and I would rather not have the $.cookie dependency. Cookies also do not work through Chrome on single-file applications without using special flags, so that's another reason for this.

I've added a config option and refactored out the get/set/remove methods for the cookie. Let me know if you need anything changing.

(P.S. I'm managed to actually edit the source this time :))