Automatically derive input reading frequency from file

[BramDr]

Currently, the frequency at which input parameters are read from file is hard coded in the model. For example the yearly land-surface inputs:

        # - assumption: annual resolution
        if self.noAnnualChangesInLandCoverParameter == False and self.dynamicIrrigationArea == False and \
          (currTimeStep.timeStepPCR == 1 or currTimeStep.doy == 1):
            msg = 'Read land cover fractions based on the given netcdf file.'```

It would be better for this frequency to be derived from the files themselves, meaning that if a monthly file is given, data is read monthly. Moreover, if the final timestep of the input file is reached, the input data of the final timestep is re-read every year. This is not needed.