Added 'required' attribute to login.html inputs

Without adding the required attribute to those inputs, the client-side validation in the help-block below the form will never actually catch and show the error without a request being sent to the server.  By adding the 'required' attribute to each input, it takes advantage of the client-side validation and shows the error already written: ng-show="form.email.$error.required && form.password.$error.required && submitted"