* Add google application_credentials platform
* Further simplify custom auth implementation overrides
* Add test coverage in application_credentials
* Simplify wording in a comment
* Remove unused imports accidentally left from merge
* Wrap lines that are too long for style guide
* Move application credential loading to only where it is needed
* Leave CLIENT_ID and CLIENT_SECRET as required.
* Prepare google calendar integration for Application Credentials
Update google calendar integration to have fewer dependencies on
yaml configuration data to prepare for supporting application
credentials, which means setup can happen without configuration.yaml
at all. This pre-factoring will allow the following PR adding
application credentials support to be more focused.
* Add test coverage for device auth checks