Support App Engine and Docker

This new version uses general cloud services intead of specific old App Engine ones. Thus, although dependant on services of Google, it's possible to run in App Engine as in Cloud Run and other containers. Also contains minor modernizations.
It runs as a normal Go application in local development, with minor need of support of gcloud tools, as datastore emmulator.
There will be effective investment on protocols rigors.
This version runs effectively, although is in consistently dev mode. All APIs may change and some services as Memcache and Search were deactivated and not yet substituted.