Added remark above the current database schema on how to create the timestamp
objects.

Replaced references to presentation.{date,startTime,endTime} that use strings
with QDateTime objects.

Modified the rss and csv reading functions to cast the presentation timestamp
fields into QDateTime objects.

Modified the csv and rss exporting functions to cast QDateTime objects into
strings.

Updated several database queries to use Date and DateTime variables instead
of just using DateTime.

Added prepared queries to replace existing queries involving the date. This was
needed since format does not work with a QDateTime object.

fix #667