SSB-47: including calibration table used for the observation and the one derived after the holography calibration

- included function to load from hdf5 file
- error handling when loading from file
- frequency axis generation
- derive new calibration table from existing one
- relative tests

SSB-47: parsing header values and implemented read function to obtain a dict object with the station and mode as keys

SSB-44: fixed python 3 and made a proper dockerfile to build the docker image to do the holography calibration

into account of the two HBA sub arrays

It is clear that reading of the holography observation in the test
data directory is supposed to be tested.  Hence just read it and
make sure that the content has been read correctly.