Enhancement: Getter for if a notification is active

[RockySouthpaw]

Suggestion 1

• Getter for if a persistent notification is active or not with a specified ID.
  • Currently you just clear it just in case its active which results in:
    . This would resolve this use case.

Suggestion 2

• Clear or hide all notifications.
  • In the event you're entering a photo mode and you don't want any, this would ether clear them all or hide them. Helpful if you're using a resource that isn't the one creating them and you wanna cover edge cases of where you want none on the screen.

[BombayV]

Added in #21