Introduced functionality to save and load customcert templates

Note: I did not create a db/upgrade.php script to add the new database tables as this module should not be currently used by anyone.
Set the default values for each page to the dimensions of an A4 piece of paper
Used the moodle_url class rather than $CFG->wwwroot for links
Removed return statement that prevented the rest of the script from executing
Added the ability to specify the PDF protection

Note: I did not create a db/upgrade.php script to add the new database column as this module should not be currently used by anyone.