* Create Tensorboard web-app backend
Create the code for the Tensorboard web-app backend which
includes routes for GET, POST and DELETE requests.
The backend is created with Python/Flask, so it also uses
the common code from 'kubeflow.kubeflow.crud_backend'.
* Add 'get_age(k8s_object)' function to 'crud_backend' common code
It would be useful for all web apps of the 'crud-web-apps' folder
to return age information to their frontends.
As a result, 'get_age(k8s_object)' was added to the common code,
so that all web apps can use it.
f55c0d77dc