Refresh access token during sensor startup
This PR closes #2 (closed) and partially fulfils #1 (closed).
There are three main changes in this PR:
- glow.py is no longer flagged as async capable
- Calls to glow.py are wrapped in hass' async helper
- Sensor setup can detect & recover from expired access tokens
Unfortunately, this still requires the user to restart hass or otherwise reload the component, so there's a bit more work to be done on #1 (closed).