Changed event handler properties to use lists of callbacks
Added add/removeEventListener and handled the list of callbacks
Minor bug fixes
Added test and fixed up existing test
Adding handlers already present should not be added again
Updated interaction between addEventListener and onevent
Improved testing for onevent and addEventListener behaviour
Minor review changes
Recycle event object across callbacks
Logic error
Expanded array loop
Rearranged code
Updated timing input names
Use timed item as this in onevent handler call
Merge pull request #420 from alancutter/addEventListener

Implement addEventListener and removeEventListener interface on TimedItem