disable buttons for large courses on legacy and beta instr dash

set max enrollment for downloads to 200

lms/templates/courseware/instructor_dashboard.html

@@ -173,8 +173,8 @@ function goto( mode)
     </p>
 
     <p>
-    <input type="submit" name="action" value="Download CSV of answer distributions">
-    <input type="submit" name="action" value="Dump description of graded assignments configuration">
+    <input type="submit" name="action" value="Download CSV of answer distributions" class="${'is-disabled' if disable_buttons else ''}">
+    <input type="submit" name="action" value="Dump description of graded assignments configuration" class="${'is-disabled' if disable_buttons else ''}">
     </p>
     <hr width="40%" style="align:left">
 
@@ -369,9 +369,26 @@ function goto( mode)
 %if modeflag.get('Enrollment'):
 
     <hr width="40%" style="align:left">
-    <p>
-    <input type="submit" name="action" value="List enrolled students">
-    <input type="submit" name="action" value="List students who may enroll but may not have yet signed up">
+    <h2>${_("Enrollment Data")}</h2>
+    % if disable_buttons:
+
+    <div class="msg msg-warning">
+      <div class="copy">
+        <p>
+          ${_("Note: some of these buttons are known to time out for larger "
+              "courses. We have temporarily disabled those features for courses "
+              "with more than {max_enrollment} students. We are urgently working on "
+              "fixing this issue. Thank you for your patience as we continue "
+              "working to improve the platform!").format(
+              max_enrollment=settings.MITX_FEATURES['MAX_ENROLLMENT_INSTR_BUTTONS']
+            )}
+        </p>
+      </div>
+    </div>
+    % endif
+
+    <input type="submit" name="action" value="List enrolled students" class="${'is-disabled' if disable_buttons else ''}">
+    <input type="submit" name="action" value="List students who may enroll but may not have yet signed up" class="${'is-disabled' if disable_buttons else ''}">
     <hr width="40%" style="align:left">
 
   %if settings.MITX_FEATURES.get('REMOTE_GRADEBOOK_URL','') and instructor_access: