Telegram: Allow admin to add telegram contact

Works in the same way as on the form, but can now be done in the
accounts tab.

ts/typings/d.ts

@@ -4,6 +4,8 @@ declare interface Modal {
     show: () => void;
     close: (event?: Event) => void;
     toggle: () => void;
+    onopen: (f: () => void) => void;
+    onclose: (f: () => void) => void;
 }
 
 interface ArrayConstructor {
@@ -98,6 +100,7 @@ declare interface Modals {
     customizeEmails: Modal;
     extendExpiry: Modal;
     updateInfo: Modal;
+    telegram: Modal;
 }
 
 interface Invite {