Improve explanation of user interface fundamentals

[amyjko]

Feedback from a student:

• Maybe instead of talking about inputs, algorithms, and outputs before states and event handlers seperately, integrate them into one example, I think that it was kind of weird to transition from Google to alarm clocks. I think it might be better to introduce all of the terms in one example, and then reiterate them in the second example ratehr than introduce some in one example and the rest in the other example.
• I don't think the distinction between state and mode was clearly explained
• Hidden affordances are not really explained--I still cannot even guess what they are since it seems like a bit of an oxymoron (but I looked them up)