MOODLE_INTERNAL check

Hello,

First of all I want say thank you for your work with the plugin.

I just would like to suggest, that it would be good to add MOODLE_INTERNAL check in php file apply/lib.php in the plugin to comply Moodle code requirements: https://docs.moodle.org/dev/Coding_style#Require_.2F_include.

Best regards,
Olena Tatarintseva