Indicate that an event is a sub-event on the main page

[aaronpk]

Currently there is no indication that an event is a sub-event on the main page. We need some visual indicator that this is part of a larger event.

Sub-events should always be contained within the time range of the main event, so we could consider nesting them under the main event. However, it is possible that another event will happen in between two sub-events that is not part of the main event, so nesting could cause confusion since the list would no longer actually be in time order.

Also keep in mind that sub-events might be all short sessions within one day, or could be full-day events within a week-long event.

[dshanske]

Temporary solution...indent them.