feat(CLI): per-API-credentials with default

That way, we can provide better service, as CLIs that consume a lot of
quota can easily have their own app credentials, and with it, their
own quota.

The fallback will be a project that allows to use all possible
google APIs.

The user can always put in his own application secret to use his own
quota or even paid services.

Fixes #80

etc/api/shared.yaml

@@ -1,4 +1,5 @@
 api:
+  credentials: "{\"installed\":{\"auth_uri\":\"https://accounts.google.com/o/oauth2/auth\",\"client_secret\":\"hCsslbCUyfehWMmbkG8vTYxG\",\"token_uri\":\"https://accounts.google.com/o/oauth2/token\",\"client_email\":\"\",\"redirect_uris\":[\"urn:ietf:wg:oauth:2.0:oob\",\"oob\"],\"client_x509_cert_url\":\"\",\"client_id\":\"620010449518-9ngf7o4dhs0dka470npqvor6dc5lqb9b.apps.googleusercontent.com\",\"auth_provider_x509_cert_url\":\"https://www.googleapis.com/oauth2/v1/certs\"}}"
   blacklist:
     # exclude APIs which currently don't build correctly. State the reason for the exclusion as well
     # to allow looking at it at a later point.