TableNames and Schemas share 'position' abstraction too loosely

[bhtucker]

Summary

We have a position abstraction in logic but not in our objects.

Details

Managed schemas can be promoted from one 'position' to another (ie, staging -> standard, backup -> standard).

TableNames can give their names in 'staging position', which implies a prefix if their schema is a managed schema. However, getting a 'staging' TableName involves setting a private attribute, which is bad.

The same concept as at work here, but is not documented/implemented in a way that makes the connection obvious.

[tvogels01]

This should be a "required" refactoring before we dig into falling back to old data (Issue #75). With the notion of "position" in place, deciding where to copy "old" data from will be more deterministic.