Oauth-dropins

Notable changes

* _Breaking change_: switch from [Google+ Sign-In](https://developers.google.com/+/web/signin/) ([which shuts down in March](https://developers.google.com/+/api-shutdown)) to [Google Sign-In](https://developers.google.com/identity/). Notably, this removes the `googleplus` module and adds a new `google_signin` module, renames the `GooglePlusAuth` class to `GoogleAuth`, and removes its `api()` method. Otherwise, the implementation is mostly the same.
* webutil.logs: return HTTP 400 if `start_time` is before 2018-04-01 (App Engine's rough launch window).

Notable changes
* Fix dev_appserver in Cloud SDK 219 / `app-engine-python` 1.9.76 and onward. [Background.](https://issuetracker.google.com/issues/117145272#comment25)
* Upgrade `google-api-python-client` from 1.6.3 to 1.7.4 to [stop using the global HTTP Batch endpoint](https://developers.googleblog.com/2018/03/discontinuing-support-for-json-rpc-and.html).
* Other minor internal updates.

* IndieAuth: support JSON code verification responses as well as form-encoded ([snarfed/bridgy809](https://github.com/snarfed/bridgy/issues/809)).

Notable changes

More Python 3 updates and bug fixes in webutil.util.

Notable changes
* Add GitHub!
* Facebook
* Pass `state` to the initial OAuth endpoint directly, instead of encoding it into the redirect URL, so the redirect can [match the Strict Mode whitelist](https://developers.facebook.com/blog/post/2017/12/18/strict-uri-matching/).
* Add humanize dependency for webutil.logs.

Notable changes
Mostly just internal changes to webutil to support granary v1.10.