Sort by date/time correctly in the Event List view

This patch fixes some bugs in the Event View:

• If the Event List view contains a mix of events, to-dos, and journal entries, sorting by their start date/time does not order them correctly, because the start values for to-do and journal list items are undefined.

• The sorting code does not consider recurring to-dos.

• Sorting by end date/time puts the list items in the reverse of the correct order; try sorting the end date/time column and the summary column into ascending order, and compare the up/down indicators in the column headers.