Merge pull request #799 from garethpdx/master

Removes mutable default argumens. Fixes bug #759
Add gartehtpdx as a contributor
Silence the version import error
Remove unused imports
Remove unused imports
Fix import flake errors
Get rid of mutable default arguments while I'm here.
Remove unused imports
Remove unused imports
Remove unused imports
Fix unused variable assignment
Fix unused variable assignment
Fix unused variable assignment
Silence unused import
Remove unused imports
Silence the import error
Remove unused import
Import from dataset and in init to get rid of Travis build error.
Explicitly import sqlalchemy functions and classes where needed

These have been removed from openspending/model/meta.py from which
they were magically imported. They should be explicitly imported
so maintainers will know from where these functions and classes
come instead of needing to chase them down.
Explicitly import sqlalchemy and openspending.model classes and functions

This gets celery up and running as it now imports explicitly from
the openspending.model modules (which in turn import explicitly
from sqlalchemy).

Explicit is better than implicit.