ConsoleUI class is a mess

[davidschlachter]

Important principle of programming: Don't repeat yourself

The ConsoleUI class is full of pieces that should be turned into separate methods to remove repetition. Otherwise, changes to one functionality need to be made all over the class. For example, there should be a 'getInput' class that gets user input, checks if it's valid (from an array of possible answers, or a range of doubles, etc; and if invalid, asks again), and returns it to the calling method. At present this is copy-pasted every time it happens!

Also, separating the pieces into modules makes them more testable.

[davidschlachter]

Partially addressed in 75ac68e, but see #22 and #23.

[davidschlachter]

One of our last to-dos on this right now is #30