You can now open optical data in PressureAnalysis and apply a smoothing
operation to the data. For this PressureAnalysis had to be generalised to
take any sort of BasePotential as a reference signal. Taken some functions
out of Unemap and put them in to BasePotential so that they can be
accessed by the Optical class. In the process of creating a new figure
called ThresholdData which inherits from SelectData. This will involve
some changes to SelectData that might not work.