hide empty management list selector, add explanation text

lms/static/coffee/src/instructor_dashboard/membership.coffee

@@ -463,6 +463,8 @@ class Membership
         text: auth_list.$container.data 'display-name'
         data:
           auth_list: auth_list
+    if @auth_lists.length is 0
+      @$list_selector.hide()
 
     @$list_selector.change =>
       $opt = @$list_selector.children('option:selected')

lms/templates/instructor/instructor_dashboard_2/membership.html

@@ -54,6 +54,14 @@
 
   <div class="request-response-error"></div>
 
+  %if not section_data['access']['instructor']:
+    <p>
+      Staff cannot modify staff or beta tester lists. To modify these lists,
+      contact your instructor and ask them to add you as an instructor for staff
+      and beta lists, or a forum admin for forum management.
+    </p>
+  %endif
+
   %if section_data['access']['instructor']:
     <div class="auth-list-container"
       data-rolename="staff"
@@ -68,7 +76,6 @@
       data-add-button-label="Add Staff"
     ></div>
 
-    %if section_data['access']['instructor']:
     <div class="auth-list-container"
       data-rolename="instructor"
       data-display-name="Instructors"
@@ -79,7 +86,6 @@
       data-modify-endpoint="${ section_data['modify_access_url'] }"
       data-add-button-label="Add Instructor"
     ></div>
-    %endif
 
     <div class="auth-list-container"
       data-rolename="beta"
@@ -92,9 +98,7 @@
       data-modify-endpoint="${ section_data['modify_access_url'] }"
       data-add-button-label="Add Beta Tester"
     ></div>
-  %endif
 
-  %if section_data['access']['instructor']:
     <div class="auth-list-container"
       data-rolename="Administrator"
       data-display-name="Forum Admins"