MDL-73990 mod_assign: Show the activity info and attachments

Show the activity information in the view page and add/edit submission
page.
- Removed the line change to disable activity header. This should help
    - When any additional files are attached to the assignment by the
      teacher/admin they should be displayed in the view and add/edit
      submission page (in the default settings)
- Added more padding to the "Add submission" button.
- Changed the string 'Activity' to 'Activity instructions'.

mod/assign/lang/en/assign.php

@@ -26,7 +26,7 @@ $string['activityattachments'] = 'Assignment activity attachments';
 $string['activitydate:submissionsdue'] = 'Due:';
 $string['activitydate:submissionsopen'] = 'Opens:';
 $string['activitydate:submissionsopened'] = 'Opened:';
-$string['activityeditor'] = 'Activity';
+$string['activityeditor'] = 'Activity instructions';
 $string['activityeditor_help'] = 'The actions you would like the student to complete for this assignment. This is only shown on the submission page where a students edits and submits their assignment.';
 $string['activityoverview'] = 'You have assignments that need attention';
 $string['addattempt'] = 'Allow another attempt';

mod/assign/locallib.php

@@ -4927,12 +4927,10 @@ class assign {
             $PAGE->blocks->add_fake_block($bc, reset($regions));
         }
 
-        $PAGE->activityheader->disable();
-
         $o .= $this->get_renderer()->render(
             new assign_header($this->get_instance(),
                               $this->get_context(),
-                              false,
+                              $this->show_intro(),
                               $this->get_course_module()->id,
                               $title,
                               '',

mod/assign/templates/user_submission_actionmenu.mustache

@@ -142,7 +142,7 @@
     }
 
 }}
-<div class="container-fluid mb-1">
+<div class="container-fluid mb-4">
     <div class="row">
         {{#submit}}
         <div class="col-xs-6 mr-3">