Handling for extra args in _audit method.

- Move non-reserved kwargs into extra args. This make the audit method easier to use.
Include python-json-logger
Update logging.conf to use JsonFormatter.
Update audit calls to use structured logging.
Add more fields to audit log line.
to_serializable_dict method in stormbase

- This method returns a serializable dict of the data fields of a db model object. This output of this method can be passed to json.dumps(...)
Use to_serializable json.
Add json formatted audit log handler in syslog config.
Explicitly use extra rather than generating in the _audit method.
Fix st2auth entry point.

We still want to allow user to run the st2auth as a standalone service for
testing purposes.
Improve jsexpose decorator.

If method expects a body and takes additional argument in the signature, pass
this argument to the method even if no body is provided.
Merge pull request #819 from StackStorm/bug-fixes/STORM-858/improve_jsonexpose_body_handling

Improve jsexpose body handling
Virtualenv should be created with --system-site-packages
Merge pull request #829 from StackStorm/virtualenv_fix

RFR: Virtualenv should be created with --system-site-packages
Merge pull request #814 from StackStorm/json-audit-log

Audit logs in JSON
Move exisiting controllers to v1 folder (API versioning)
Move test files to v1 directory
Update configs to use versioned APIs
Transition ActionSensor to use TriggerDispatcher.
Merge pull request #831 from StackStorm/action-sensor-updates

Transition ActionSensor to use TriggerDispatcher.