Add object support to API service.

The previous api/controllers/v1.py code was an early straw-man that
directly represented db/sqlalchemy/models.py data structures as a
proof-of-concept for the API service.

This replaces that by using the versioned object models which were
recently ported from Nova, wrapping them in an API class to allow for
type checking and versioning.

This patch also removes other methods which were part of that early
proof-of-concept, and which will be implemented according to the v1 API
spec in future patches.

It also removes the unused api/models/__init__.py and db/models.py
files.

Partially implements bp:api-v1-impl

Change-Id: I2580d863b383e12628821c9156195c00806beebd
Add support for GET /v1/nodes to return a list.

Adds the db/api and db/sqlalchemy/api methods,
and the 'get' method in the API service.

Partially implements bp:node-api-actions

Change-Id: I214687c19150e65183f663d99f165d7fdea9915f
Port middleware error handler from ceilometer API

Change-Id: I159923338e0447347d1c4bed4a80586ad6c06fcc
Merge "Add object support to API service."
Merge "Add support for GET /v1/nodes to return a list."
Merge "Port middleware error handler from ceilometer API"