Provide means to add entities to the application db using specmonstah library.

There are 4 main parts to it:
- specs for column types (id, names, emails...). Used to generate random values.
- specs for entities. Aggregations of types
- schema. Structure of the dependency graph. Used by specmonstah to create the
  entities in the right order, and to link fks between them.
- insert. 
    - Generating the entity graph, then removing the `id`s (so
      the underlying db adds them and the id's don't clash with already existing ones).
    - Adjust field values that have constraints besides DB ones.
    - insert to the db using `toucan`.