spectrapro: fix initialisation due to overriding variable

model can obviously not be used
wished pylint could warn assigning a name of a module by something not a module at all
wished even more that I don't forget to run the test suite before committing
test cam: check binning metadata
pvcam: fix wrong assert and improve min resolution computation

min resolution must depend on binning
spectrometer: add some test cases

not all test cases there yet, but already quite a few bugs fixed
spectrometer: some more test cases

still some problem with wavelength conversion