[deploy,app.yaml][s]: switch to python 2.7 runtime and document deployment.

* python 2.7 change required as dataconverters uses import json and that is not supported by python 2.5
* Note also change in app id to jsonpdataproxy-hrd this was because:
* python 2.7 only supported on GAE with new HRD datastore (we don't use the datastore but we still need to upgrade). This required a migration as per https://developers.google.com/appengine/docs/adminconsole/migration and a new app id (though note the old app id is now automatically handled by new app so no breakage there!)
[vendor/messytables][xs]: latest messytables which removes use of tempfile for xlxs (essential for GAE).