MDL-57898 core_customfield: Custom fields API

This commit is part of work on Custom fields API,
to minimize commit history in moodle core the work of a team of developers was split
into several commits with different authors but the authorship of individual
lines of code may be different from the commit author.

lib/classes/plugin_manager.php

@@ -1740,6 +1740,10 @@ class core_plugin_manager {
                 'gregorian'
             ),
 
+            'customfield' => array(
+                'checkbox', 'date', 'select', 'text', 'textarea'
+            ),
+
             'coursereport' => array(
                 // Deprecated!
             ),