GUAC-1176: Provide user with help text during login. Style continuation dialog differently. Add continue button.

guacamole/src/main/webapp/app/login/directives/login.js

@@ -35,6 +35,14 @@ angular.module('login').directive('guacLogin', [function guacLogin() {
     // Login directive scope
     directive.scope = {
 
+        /**
+         * An optional instructional message to display within the login
+         * dialog.
+         *
+         * @type String
+         */
+        helpText : '=',
+
         /**
          * The login form or set of fields. This will be displayed to the user
          * to capture their credentials.