Resolve "ProjectServer accessors."

Closes #41 (closed)

app/db/accessors/__init__.py

 """SQLAlchemy accessors for the resources managed by the admin database."""
 from .dataset import dataset_accessor as dataset
 from .project import project_accessor as project
+from .project_server import project_server_accessor as project_server
 from .table import table_accessor as table
 
 __all__ = (
+    'project_server',
     'project',
     'dataset',
     'table',