Real time updates

[Perelandra0x309]

This may be a stretch, but in Haiku when changes are made it is preferable that changes are updated in real time. So for example if I change the category the event color is instantly changed in the Calendar window. This does rquire some changes though

1- Remove the "Save" button since it won't be needed if changes are saved automatically
2- Replae the "Cancel" but with "Revert" to revert the changes made since editing this event started.

See the Mouse preferences as an example.