Added stimulus fixation

Shows a fixation stimulus for the whole trial
Added tactor class for interfacing with tactors

This is designed for use with tactors from Engineering Acoustics, Inc.
The communication is via the serial port, using the psychtoolbox
function IOPort. The tactor class can be used without the rest of
RepeatedMeasures
Added tactors

Added tactors to experiment / trial. You need to define the sequences in
the setup section, then in each trial there can be 1 or more tactor
events