Add App Engine Standard app for proxying API requests.

gae-service-proxy is a barebones App Engine app that will forward requests
to App Engine only APIs. This is secure because it does not authorize the
requests it forwards.

Change-Id: I8b248d1a97784ef759dc010f00893ba4748efb0d
Reviewed-on: https://go-review.googlesource.com/38398
Reviewed-by: Tuo Shan <shantuo@google.com>
2 files changed