1. Improved documentation. Every plugin now reports the exact steps to
get the integration up and running with the right API scopes.
2. All Google plugins now have a standard process to get (and reuse) the
client secret. Except for PubSub, Translate and Maps (which have
their own flows), all the Google plugins now read the client secrets
from `<WORKDIR>/credentials/google/client_secret.json` by default.
3. Black/LINT for some of those plugins, which hadn't been touched in a
while.
4. The interface to pass API scopes is now leaner. It's now possible to
pass a scope directly as e.g. `calendar.readonly` rather than
`https://www.googleapis.com/auth/calendar.readonly`.
5. Improved the logic to retrieve the right scope tokens file. If e.g.
an integration requires the role `A`, and a credentials file exists
for the roles `A` and `B`, then this file will be used rather than
prompting the user to authenticate again.