Added function for loading arrays

* Created loadArray function, which swaps arrays into spriteArray, then
edits the height and width of the canvas to match the sprite.
* Added second paragraph and an unordered list of images, to use as the
sprite selector.
* Added event listeners to the image elements.
* Did a little DRYing out of the copyArrayToCanvas() function.

To do:
* The sprite swapper still isn’t working — need to fix it.
* Add unit tests in Jasmine.