Handle partial time values (#4)

Comments? These commits add the following:

1. html5 validation using `pattern` attribute on date and time fields. This enforces the required format but doesn't necessarily come with intuitive warnings for the user
2. an `onchange` event handler that detects abbreviated time formats like '15' and changes them to '15:00'

Does the second case go far enough? Should '7' become '07:00'? Should '730' become '07:30'?
Should we be doing anything similar for dates?

ps: Should firefox implement date and time controls? Yes it should :)