Save and Delete: make calls on object

this brings the save / delete calls onto the CNXBase objects.  Previously we
used the recommended SQLAlchemy way of magically having dbsession in module
namespaces.  I have explicitly passed the dbsession now into save call, so
avoids a little bit of magic.  (We still deal with the magic of SQLA)
Merge pull request #112 from Connexions/save-delete

Save and Delete: make calls on object