#25569 unix timestamps are now converted before being passed to hook.

The unix timestamp handling is to mitigate various shortcomings in the
QT/PySide/SG API serialization capabilities and means that all time
stamps in the model data are cached as unix timestamps (number of
seconds since 1 Jan 1970 in UTC time zone -
http://en.wikipedia.org/wiki/Unix_time). This means that all data
currently being returned by the sg model comes back with this time data
format rather than the standard SG Time stamp. (there is no easy way to
slap an interface around the return data). 

This fix converts these unix timestamps back to sg timestamps prior to
passing shotgun data to the action hooks, making it more familiar for
TDs and developers.
added better docstrings.