Add link to the "Accessibility Statement for Moodle App"

This is mandatory (according to some EU policies) it could be in the about of the app, just after the privacy policy (and before the feedback)

Please notice that this statement is only for the official Moodle Mobile app, com.moodle.moodlemobile, so it should not be displayed in other custom apps.

Link text: Accessibility statement

The link: https://apps.moodle.com/admin/tool/policy/view.php?versionid=5