various updates

added adjustment for probe tip pressure — essentially a pre-run
calibration for the prop sensor to probe tip pressure sensor.

fixed parameters in pressureSensor structure inits (was setting as kPa,
should have stuck with psi).

added proportionairPressure pressure function (copied from v1 of code).

fixed timeout in receiveElectrodePairs function.

redo of BLINK_INTERVAL statements for while running test or waiting for
second button press.