Allow binary sensor state to be None

[frenck]

Breaking change

Previously, binary_sensor entities could have the state on or off, and in case the device was unreachable: unavailable. However, compared to other entities, it wasn't able to have the unknown state, which has been added.

So, a binary_sensor entity can now have the on, off, unavailable, or unknown state.

You might need to adapt your automations or scripts to take this new unknown state into account.

Proposed change

Binary sensors currently cannot have a None state value (which translates to an "unknown" state). This PR adjusts that.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request: Allow binary sensor state to be None developers.home-assistant#1161

Checklist

• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

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• Documentation added/updated for www.home-assistant.io

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  Updated and included derived files by running: python3 -m script.hassfest.
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[elupus]

Looks good i think. At least from rfxtrx perspective.

[frenck]

Rebased to deal with a merge conflict in the tasmota integration