Fixes keyboard input bugs.

When using keyboard input, HTML5 apps need to call
`e.preventDefault()` and `e.stopPropagation()` to keep key events
from bubbling up to the browser and triggering built-in shortcuts.
Particularly noticeable in browsers with typeahead find, where
pressing any key focuses the find-in-page search box.
Merge pull request #10 from mildmojo/fix_key_controls

Fix keyboard input bugs