blocks: MDL-19399 proper permissions checks for editing blocks.

In particular for editing sticky blocks. If the admin addes one at site level,
then the teacher should not be able to change its configuration from
the course page, but should be able to set the position on this page.

blocks/edit_form.php

@@ -121,6 +121,14 @@ class block_edit_form extends moodleform {
 
         $mform->addElement('select', 'bui_weight', get_string('weight', 'block'), $weightoptions);
 
+        $pagefields = array('bui_visible', 'bui_region', 'bui_weight');
+        if (!$this->block->user_can_edit()) {
+            $mform->hardFreezeAllVisibleExcept($pagefields);
+        }
+        if (!$this->page->user_can_edit_blocks()) {
+            $mform->hardFreeze($pagefields);
+        }
+
         $this->add_action_buttons();
     }