Event End Date Should Be Optional

Currently, the End Date is a required field when creating a new event. Some events do not have defined end dates, so this field should be optional.

You will need to review the code and display / output for the following functionality to verify reasonable behavior when end date is NULL:

• Event Info page ("When" display should just show start w/ "through")
• Event confirmation email
• iCal output - DTEND element should not be included if end date is null
• RSS output