[ChaosDatastore]Checkin latest version of the app engine code

Get all the working code and add date-util package to requirements and a README.

Bug: 112916493
Test: Tested locally and with the gcloud server
Change-Id: I5e8e31ef44bc0d6827de926d8d39e125653273f4
Reviewed-on: https://chromium-review.googlesource.com/1183818
Tested-by: Bindu Mahadev <bmahadev@chromium.org>
Reviewed-by: Bindu Mahadev <bmahadev@chromium.org>
Reviewed-by: Kris Rambish <krisr@chromium.org>
Commit-Queue: Bindu Mahadev <bmahadev@chromium.org>
Trybot-Ready: Bindu Mahadev <bmahadev@chromium.org>
8 files changed