1.2.0

New features:

• Runs a coordinator that checks Mattermost connectivity every 5 minutes. Previously if the Mattermost server went offline, the component would just silently fail (well, it would put an error in the log).
• Adds a new entity (binary_sensor) for Mattermost server connectivity.
• Marks the integration as failed after a few missed connectivity checks.
• Backs off exponentially but still tries to reconnect.