Fixes issue #2 around date fields for cases.

Added three new fields for a FogBugz case:

DateOpened
DateResolved
DateClosed

Required a little rework of code generation for mapping DateTime types.
Changed all source object (i.e. FogBugz native objects) that are usually
of type DateTime to be string. The destination objects being exposed
still have DateTime types.  However, our use of AutoMapper properly
handles empty dates incoming from native FogBugz Api and sets the
destination to be null, which AutoMapper converts to DateTime.MinValue.