Measure calculation script

Added the `cat_3_calculator.rb` script, some changes to make it work (added a `measure_eval` session to `config/mongoid.yml`), and the changes to use it in `measure_evaluation_validator.rb`. The script still currently skips over CMS117v3, the Childhood Immunization Status measure, as the changes necessary for that measure to properly calculate are not yet in the bundle.

Also made some minor refactors to the measure evaluation script to improve the efficiency of cat I and multi-measure Cat III testing.