Migrate to using fixed permissions

When deciding which app/group/channel level fields are editable. If
an app has a fixed notification permission, no importance type fields
(including blocking, importance, minimizing, popping on screen, or
prioirty conversions) can be edited.

Test: Robotests
Bug: 194833441
Change-Id: Idc198ea05cd2ab6e43387ae4e8290f446ccfa0c6