Modified the username and email duplication error (1641).

	- changed the route for retrieval of existing username and emails.
	- renamed the hasError method of createAccount.js to formIsOkay.
	- added a method emailExists for duplication errors.
	- removed the username route and usernameCheck method of user.js
	- added basicFieldValues method in users.js for retrieval of existing usernames or emails.