Automatically apply workaround for Dvorak-Qwerty keyboards on OS X

Fixes #12

This applies @donmccurdy's approach of reading the keyCode instead of the keyIdentifier when the active keymap is Dvorak-Qwerty on OS X. It uses native APIs to detect a layout switch so it should not require user intervention to make this layout work.
Should this go in the Properties section with the other private properties? Line 90