Introduced customisable elements to the customcert

Elements are sub-plugins that have the same abilities as a core plugin, such as creating tables, capabilities and performing upgrades.

Currently elements can define -

* What additional form elements are rendered when adding the element to the customcert customisation page.
* How the data from the additional form elements is validated and saved.
* How the element is rendered on the PDF.
* How the element handles removing data when it is deleted.

mod_form.php

@@ -52,7 +52,6 @@ class mod_customcert_mod_form extends moodleform_mod {
 
         $this->add_intro_editor(false, get_string('intro', 'customcert'));
 
-        // Design Options.
         $mform->addElement('header', 'options', get_string('options', 'customcert'));
 
         $mform->addElement('text', 'requiredtime', get_string('coursetimereq', 'customcert'), array('size' => '3'));