Refactor the ExtraMark model to be Rails 4 compatible

And also eliminate the need for the ExtraMark::UNITS hash lookup.
Second volley of Rails 4 model updates

This includes updating various queries for Rails 4 in a way that is
backwards compatible with Rails 3.

This also includes some small cleanups, and some model constraints
have been reordered to group the subject of the constraint.
Merge branch 'finders' of https://github.com/ferrous26/Markus into finders

Conflicts:
	app/controllers/results_controller.rb