Rewrite of webapp2 auth section needed

[Fili Wiese]

Created an issue to support the new standard GAE Python3 with webapp2: https://github.com/GoogleCloudPlatform/webapp2/issues/137

It needs a complete rewrite of the auth code as NDB, memcache and Users API are not supported anymore in the next generation GAE.

In addition, Google is moving from NDB and GAE Datastore to Firestore (although they support for the time being backwards compatibility with Cloud Datastore, this will still run on Firestore). So the codebase needs to migrate to either Firestore or become database independent and have adapters for the different database solutions. 

If you want to get started with webapp2 on the new standard GAE Python3 with webapp2, try https://bitbucket.org/fili/gae-standard-python37-webapp2-example/src/default/