UX: When a policy reminder notification is sent mark it as high priority (PR #12)

This is so policy reminders do not fall by the wayside. They are given the same priority as bookmark reminder and PM notifications, so they show with the green notification bubble.

NOTE: The PR https://github.com/discourse/discourse/pull/9660 MUST be merged first!


oh … before creating this notification be sure you delete the old one.

This thing nags once a week or once a day, no need to clutter notifications with dupes

@SamSaffron added the delete!

looks good to me, feel free to merge.