Schedule support for all day events

There is currently no specific way of handling all day events. My implementation uses the times 00:00 to 23:59 to represent such an event, although other implementations may have a boolean flag. There are two problems this causes. Firstly, the start and end time are rendered in the month and week views. This is not good for a user to have to see the internal start and end time. Secondly, the new variable day length feature automatically, and unnecessarily, expands the day to the full 24 hours when there is an all day event.