Talk times are not updated

[kaymckelly]

Default number of minutes is not being used to set the talk times or validate that the talks fit in the time slot. Currently we have a heuristic that gives a warning when you add too many talks to a time slot.

[kmccurley]

There are actually many issues surrounding how talk times are handled:

1. start time should be before end time. duh
2. talk time should be within session time.
3. when a talk is unassigned, it should lose it's times.
4. shared speaking timeslots are an abomination.