pin to given psycopg2 version.

We are using "with" keyword and that available in this version, not previously
Use ini file to define postgres connection string
Direct sql calls for content and folders
Fixed up folder.contents (which returns a list of {id, title, mediaType}
Removing references to the sql alchemy models
Validated design, needs reintroduction of models
Merge pull request #167 from Connexions/remove-sqlalchemy-rebased

Removes SQLAlchemy