Using `require` didn't make much sense since most of them are only used in a single place anyway, and it takes care of a few weird interactions in the process (besides not polluting `package.loaded` with useless crap ;)).
* Add a basic Japanese keyboard layout
Allow for entring Japanese text into text boxes. Only supports kana
and latin letters due to limitations of current VirtualKeyboard
implementation (complex text input with conversion is not possible).
* Allow keyboard layouts to declare custom modifiers
Refactor modifier key setup code and existing keyboard layouts so
that each layout can declare custom modifier key labels. This
allows for greater extensibility and for future keyboard layouts.
