Improve integration of the new storage code and provide a new SQLAlchemy backend

by Christopher Denter for MoinMoin Wiki

As of last years GSoC, MoinMoin got a new abstraction layer for storage of data. That storage layer is not yet fully integrated. This proposal aims to improve the situation by adding things like support for ACLs and a routing middleware that can be used to set up different backends for different 'namespaces'. Additionally, a new backend will be provided that uses the SQLAlchemy library to store data in one of several supported database formats (SQLite, Postgres, MySQL, ...).