Gain ref for k2DriftTracker; doc for SimpleRSPicker

Added normalization by a gain reference to k2DriftTraker.  Updated the
doc file CommandsForRSPicker.rtf
Improved SimpleRSPIcker

Fixed a bug in SimpleRSPicker which identified inside-out particles
outside the appropriate region.  The main changes are in
rsVesicleCorrelation5.m Also changed the variance calculation to occur
inside rspLoadFiles.