Add support for creating collections of models

[mttkay]

A feature we're missing is the ability to create more than one model at a time. We often use ModelCitizen to create pages of items, and right now we have to write our own test helper that invokes createModel in a loop.

What we should be able to do instead is something like:

List<Model> items = factory.createModels(Model.class, count)

This could be quite powerful in tandem with the existing suggestion to provide test helpers that specify how to generate ranges of field values

[mguymon]

:+1: