First round of adding changeset operations

Adds changesets_get, changeset_create, and
changeset_get_by_pk functions to the DB API.

Partially Implements Issue #52
Merge pull request #54 from jaypipes/changesets

First round of adding changeset operations
Fix pep8 errors
Add DELETE changeset operation to DB API
Start of object validation cleanup
Add schemas for user and group.
Add schema for user public key.
Add schema for domain.
Add schema for repository.
Add schema for changeset.
Add schema for change.
s/datetime/date-time/ for schemas
Saving progress on jsonschema branch..
Major refactoring around objects and DB API

Changes create methods in DB API for organization and group to use
objects -- which have validation built in to them. In the process, we
changed from UUID identifiers to integer identifiers, for scale and
performance reasons, as well as human-readability.

Moves objects out of procession/api/ and into the main procession/
namespace, and moves some of the serialization base routines out of the
api helpers and into the main procession helpers.
Merge pull request #4 from jaypipes/jsonschema

Major refactoring around objects and DB API