Add voltracker api version display application

At present, the api only has its first version to support
Add the authentication step to api flow

voltracker is design to support both the unauth and keystone-auth
methods, but the unauth is the default.
most of the code is ported from glance.
also add the missing api/v1/__init__.py and api/__init__.py
Auth context rename

rename AuthContextMiddleware to ContextMiddleware.