MQTT notification when Birdseye is active

**Describe what you are trying to accomplish and why in non technical terms**
I want to be able to detect when Birdseye is active so that I can cause tablets to display Birdseye only when it is active.

**Describe the solution you'd like**
An MQTT notification when Birdseye becomes active and when Birdseye becomes inactive.

**Describe alternatives you've considered**
I created a sensor of the same entities that Birdseye watches, but it has been unreliable.

The issue names no files, tests, or entry points. Start by locating the Birdseye activity state and the existing MQTT notification code, then define the active and inactive events and verify that both transitions are published.

Written by the indexing model from the issue text.