* The button to "Add group/grouping access restriction" under
   common module settings should only be present if corresponding
   availability plugins are enabled; and
 * Prevent the same button behaving as a submit button, which
   intercepted the user hitting return in the form and added a
   restriction without deliberate action taken by the user.

The %P modifier is not supported in the macOS (MDL-71549)

1) The GROUP BY statement must include all fields in the SELECT
   not being aggregated or constant cols.
2) There was a missing space causing problems to databases
   using named parameters.

In order to allow for correct seb:// or sebs:// calls without browser
warnings of insecure links, it is not possible to send a get request
with an attached cmid parameter to the unknown seb:// or sebs://
URL via a form button.
We've got to use a <a href> link outside a form to circumvent
browsers warning of an insecure link and call Safe Exam Browser
correctly.

Change the yes/no dropdowns to a checkbox. Defaults to unchecked.

In master, fixed to 2021052500