Requests for comment/Associated namespaces/Database schemas

Preliminary notes
See: User:Skizzerz/Namespaces

New database schemas

 * New namespace table needed to hold namespace relational data, based on previous work by Skizzerz.
 * Cannot guarantee that a talk namespace number will directly follow the namespace it is tied to, so this change needs to be reflected in code.


 * Index nl_namespace_name on nl_namespace and nl_name
 * Unique index nl_namespace_default on nl_namespace and nl_default


 * Type of namespace from a predefined list.
 * Possible options: talk, documentation, schema, data-item, dataproperty...