GUACAMOLE-292: Add support for email fields.

guacamole/src/main/webapp/app/rest/types/Field.js

@@ -75,6 +75,14 @@ angular.module('rest').factory('Field', [function defineField() {
          */
         TEXT : 'TEXT',
 
+        /**
+         * The type string associated with parameters that may contain an email
+         * address.
+         *
+         * @type String
+         */
+        EMAIL : 'EMAIL',
+
         /**
          * The type string associated with parameters that may contain an
          * arbitrary string, where that string represents the username of the