‘Upgrade’ from Python 2.7 to Python 3.7

Python is a non-issue.  But App Engine took the opportunity to change everything.

appengine/.gcloudignore

@@ -0,0 +1,23 @@
+# Do not upload these files.
+.*
+deploy
+*.soy
+static/appengine/
+static/closure/
+static/demos/plane/soy/*.jar
+static/demos/plane/xlf/
+static/externs/
+static/i18n/
+static/msg/json/
+static/node_modules/
+static/package/
+static/theme_scripts/
+static/typings/
+
+static/build.py
+static/gulpfile.js
+static/jsconfig.json
+static/LICENSE
+static/package-lock.json
+static/package.json
+static/README.md