Add voice command support with new voice-assistant entity

[zehnm]

Support Google voice commands.
The Android TV device needs to support voice commands. This is returned as a feature flag after connection.
This is a preview feature and needs to be enabled in the setup device configuration.

Requirements:

• new https://github.com/unfoldedcircle/integration-python-library release for voice-session support. Currently in development in the feat/voice branch.
• Remote firmware 2.8.2 or newer. Does not work with 2.8.1.

Audio-stream workaround:
For improved text recognition the audio chunks are accumulated, then sent at once to Android TV when the stream ends (releasing the microphone button).
Something is off with chunked streaming and doesn't work reliable yet.

Further changes:

• Refactor entity handling in driver.py to support multiple entities per Android TV.
  Based on the remote-entity PR Added remote entity in addition of media player entity #90
• Fix default media type and media information handling if Chromecast is enabled.
• Fix log and entity state update flooding when using Chromecast feature

Closes #87

[zehnm]

Tested with Nvidia Shield TV and Google Chromecast.
Let's hope the other Android TV devices work the same...