Schema and data comparison tools

[davenquinn]

As shown in #60, it'd be useful to have a few tools at our fingertips that allow us to compare both schema and data within tables, with the goal of quickly assessing whether/what changes exist between database versions (especially versions of the Macrostrat database in different environments).

We've already got some integration with schema-diffing capabilities (e.g., migra) but it would be nice to integrate a data-comparison tool such as PGDataDiff. This would potentially help us quickly evaluate whether foreign keys, etc. are retained between environments.

Perhaps this could be somehow integrated into #61? We might be able to make this happen in a more general way as well.