Fix appointment group tab when editing calendar events

Fixes COMMS-1326

Test plan:
- Create a calendar event
- Click on the event and edit it, verifying that there is no "appointment
  group" tab
- Make sure there are no side effects- i.e., "appointment group" doesn't
  show up anywhere else, but the tab still appears when creating a new
  event

Change-Id: I6cf44f915330a90c8f06cf06321b70b156690a40
Reviewed-on: https://gerrit.instructure.com/157852
Tested-by: Jenkins
Reviewed-by: Landon Gilbert-Bland <lbland@instructure.com>
QA-Review: Steven Burnett <sburnett@instructure.com>
Product-Review: Sara Chadwick <schadwick@instructure.com>

app/coffeescripts/calendar/EditEventDetailsDialog.js

@@ -120,7 +120,8 @@ export default class EditEventDetailsDialog {
   canManageAppointments = () => {
     if (
       ENV.CALENDAR.BETTER_SCHEDULER &&
-      _.some(this.event.allPossibleContexts, c => c.can_create_appointment_groups)
+      _.some(this.event.allPossibleContexts, c => c.can_create_appointment_groups) &&
+      (this.event.eventType.match(/appointment/) || this.event.eventType.match(/generic/))
     ) {
       return true
     }