Consolidated exercise type. Added data structures and test classes.

I removed the separate classes for Cardio and Resistance, and
consolidated all of the exercises into one Exercise data type, as their
functionality for this project is identical. I implemented an ArrayList
using a primitive array that I will be using to store exercises by
muscle groups, as well as some initial test cases. I also implemented a
queue using a LinkedList, that will be used to go through randomly
selected exercises one by one, and I added some initial test cases for
the queue as well.