blueprint api-framework-essex

blueprint api-framework-essex

Addressing Dan's comments.

This changeset provides:
- improved framework for API versioning, with separated controllers for each API version
- Taken from nova:'Resource' class in WSGI framework. This class is a container for serializers, deserializers and controller
- Better deserialization thanks to resource class. _parse_request_params has been removed
- Improved management of HTTP client errors
NOTE: this changeset does not update the framework used by API extensions.

Change-Id: I88a669ce418225c415e0da22e951762d0708e0a5