Add disabling of drag/resize for individual events

This is my proposed solution to [issue 174](http://code.google.com/p/fullcalendar/issues/detail?id=174) in the bug tracker.

This implementation allows `disableDragging` and `disableResizing` properties to be specified for specific events.  These properties can already be specified at the calendar level.  This is similar to the `editable` property that can already be specified at both the calendar and event levels.

This is a completely backwards compatible feature.