Renamed BeerSorter model and changed Beer Controller to reflect change

Gave responsibility to find beers to the new model which then sorts them
based on image availability.
Fixed variable names leftover from previous iteration of method
Changed method parameter from resembling an instance variable to a variable
Added spec for find_beers method

Checks that the result contains beers with a category that match the genre
used to initialize the BeerPrioritizer.  In the process of doing so, found and fixed a typo in the model.
Wrote tests to check the sorting ability of BeerPrioritizer
Merge pull request #116 from fence-lizards-2014/beer_sorter_spec

Beer Prioritizer refactor and spec