new: support metadata kind email

public/javascripts/control.js

@@ -836,7 +836,7 @@
           kind:       { name: 'Kind',
                         type: 'enum',
                         description: 'Type of metadata to add.',
-                        options: [ 'Device ID', 'Start Time', 'End Time', 'Today', 'Username', 'Subscriber ID', 'SIM Serial', 'Phone Number', 'Start Geopoint' ],
+                        options: [ 'Device ID', 'Start Time', 'End Time', 'Today', 'Username', 'Email', 'Subscriber ID', 'SIM Serial', 'Phone Number', 'Start Geopoint' ],
                         value: 'Device ID',
                         summary: true } },
     };

public/javascripts/data.js

@@ -491,6 +491,11 @@ var dataNS = odkmaker.namespace.load('odkmaker.data');
                 binding.attrs['jr:preload'] = 'property';
                 binding.attrs['jr:preloadParams'] = 'username';
             }
+            else if (kind == 'email') {
+                binding.attrs.type = 'string';
+                binding.attrs['jr:preload'] = 'property';
+                binding.attrs['jr:preloadParams'] = 'email';
+            }
             else if (kind == 'subscriber id')
             {
                 binding.attrs.type = 'string';