support_CF_conventions_with_mo_netcdf

It would be good to support the CF conventions. Currently the nodata_value check and masking is done after reading and an optional transformation to other data types (as in MPR to dp). This makes it especially costly to check and trasnform. On top of that, we should also support the correct use of scale_factor, add_offset, valid_range, valid_min, valid_max and _FillValue. This task is also suitable to give the templating system of fypp a go as there is a lot of functions to be generated for all types.

The idea is to automatically check for the signal attributes and perform the operations on the variables, optionally changing types. To make it backwards compatible, the idea is to now add an optional boolean argument to the getData procedures decode_cf which we set to .true.. We additionally allow for a mask to be passed as an optional argument which will receive the masked values. For later, we shall also the appropriate options in the setData calls.