Automatically Identify database tables that do not match schema

This is a next step towards proactive schema validation:

In order to understand differences between the current database schema of an installation and the desired and expected schema, we'd like to create tooling around schema validation. In this step, we're going to build the basic framework and only implement table validation.

Table validation consists of comparing the list of available tables, and their exact definition against the desired schema.

In this iteration, it'll be enough to have a rake task to run schema validation that reports back any differences (for tables) in a summary-like fashion.