#57 enable Unison and local data to coexist

[Reece Hart]

The goal is to enable periodic updates of local instances of Unison schema and data with minimal disruption. Local schema are easy. The harder case is how to enable local data to be conceptually overlaid on Unison data. For example, imagine local sequences and predictions on those sequences while maintaining the illusion of one source/schema of sequences and predictions. Table partitioning and views are likely to help.