MDL-44613 mod_assign: Fix behat failure in classic

The link to the calendar page is missing in the navigation block in
classic which causes a behat failure in the 'Set availibility dates
for an assignment' feature. The fix includes adding the calendar block
to the Course page which can be used to navigate to the calendar page.

mod/assign/tests/behat/set_availability.feature

@@ -57,10 +57,12 @@ Feature: Set availability dates for an assignment
     # Set 'Due date' to the second day of this month at noon.
     And I set the field "Due date" to "##first day of this month noon +24 hours##"
     And I press "Save and return to course"
+    And I turn editing mode on
+    And I add the "Calendar" block
     And I log out
     And I log in as "student1"
     And I am on "Course 1" course homepage
-    And I follow "Calendar"
+    And I follow "This month"
     When I hover over day "2" of this month in the calendar
     Then I should see "C1: Assignment name is due"