Fixed a bug where min-priority were in the middle

The recent intrusiveness could elevate min priority notifications
temporarily and the reordering was also blocked while looking at it.
We're now allowing the shade to reorder if a notification updates to
min-priority.

Test: manual, add intrusive notification, update while looking at the shade to min
Change-Id: I75b23a7cbaecc8ae941d6680a924c79371c95991
Fixes: 37515606