Refactor/calculator

Split large methods with nested "ifs" into multiple methods and moved them into logical modules. Created a `calculator` folder. Moved all methods (except a thin `calculate` wrapper) into one class, `ViewCalculator`.

This wasn't easy, since everything's all tied together, but I feel better about the results. The CodeClimate score didn't improve much, but it's better organized, and there aren't as many Godzilla methods.