implement frontend for user expiry/duration

this will add an optional validity period to users, where their account
will be disabled (or deleted) a specified amount of time after they
created it.

ts/typings/d.ts

@@ -90,6 +90,8 @@ interface Invite {
     notifyCreation?: boolean;
     profile?: string;
     label?: string;
+    userDuration?: boolean;
+    userDurationTime?: string;
 }
 
 interface inviteList {