Migrate code to Swift 3

[troyshu]

I migrated the codebase to Swift 3. First, I used Xcode's automatic code migration function. Then, I fixed the remaining build errors manually, to adhere to Swift 3 syntax. I manually tested the app (on my iPhone, in the simulator for various iPhone models), everything works and looks as expected.

~~Not sure if this was introduced in the migration, but the app's design degrades a little on iPhone SE. It looks fine on other screen sizes, but I guess another todo is to make the design properly responsive.~~ Many of the commits after the "Upgrade to Swift 3" one were to make the stock price chart and date range select buttons responsive to different screen sizes and device rotation.

I also committed the updated Alamofire pod to the repo. I'm new to Swift development, Cocoapod, etc. so there's probably a bunch of cleanup that needs to be done.