Fix calibration of custom measurement chain elements
Fix: When using the custom definition of measurement chain elements in the dropdown list of the [Define Input Measurement Chain]-GUI, the given sensitivity of the MeasurementChainElement got lost.
The function ita_device_list_ITA now returns the Element and corresponding sensitivity even if the element is not in the list.
Info that you're using a custom element will be displayed with verbosity level 1, to avoid spamming the terminal.