VoiceOver support

Right now, VoiceOver support is just what we get automatically from having the terminal be rendered as a webpage. Here are some of my observations from trying to use the app with VoiceOver on:

- It's possible to scroll the WebView slightly in VoiceOver mode.
- The bug where the terminal doesn't resize when the keyboard appears initially is worse with VoiceOver, since it's harder to realize you're missing part of the screen, and very non-obvious that the way to get it back is to select the terminal and double tap.
- The slick little arrow button is entirely non-functional with VoiceOver. And it's the only way to press arrows.
- The control, tab, and escape buttons are read as "control", "tab", and "escape", which is fortunate. The "hide keyboard" button is read as "black down pointed triangle", which is less fortunate.