General configuration table for content review activities

Add a table to content review to store activity-specific configuration options for a particular provider. An "activity" is most likely an assignment, but could also be something else in Sakai that might want to use a content review service, like a forum.

Configuration properties are simple name/value pairs. A "key" uniquely identifies a configuration property, and consists of the name, an id for the activity, an id for the Sakai tool the activity belongs to, and an id for the content review provider the configuration applies to.