TableAccess trait ignores provenance table

[molpopgen]

We should be able to require an additional function for this trait if Provenance is an enabled feature.

[molpopgen]

Right now, we are specifying that Provenance is a trait and that a type implementing Provenance must implement TableAccess.

Alternatives include:

• Simply adding the Provenance trait to the prelude. This is "easiest".
• Making provenance-related stuff part of TableAccess, etc., and thus promoting it into the set of "first class" table operations.