Update wifi sensor on state changes

[dshokouhi]

Use a broadcast receiver to update the wifi sensor whenever the state has changed. This includes enabling/disabling and network changes.

Adds is_wifi_on attribute to the sensor

Fixes: #429

[JBassett]

Was this tested without having location permissions? I'm not sure what happens when you try to register a receiver when you don't have permissions.

[dshokouhi]

@JBassett so in the emulator I cleared storage for the app. Logged into my dev instance and did not grant location permssions. Then I proceeded to turn wifi on/off and the app did not crash.

What I see in logcat is 2020-08-11 12:13:59.097 8055-8110/io.homeassistant.companion.android.debug W/NetworkSM: Tried getting wifi info without permission. followed by an error for updating the sensors however the other sensors are able to update just fine. The receiver is still working actually which doesn't make sense?

Should I just add a permission check when we register the receiver to avoid this? I don't see any harm if we are able to trigger sensor updates for everything else when the wifi state changes.

[JBassett]

No need for the permission check. I'm working on a slight rework of the sensors to help eleviate some of the problems we are seeing with the dynamic updates which should take care of them being enabled vs disabled.