Missing logic in FP processing

[Guillawme]

As it is now, processing FP data with format_data(data_type = "FP") will fail if the input datasets don't contain the polarization, anisotropy and intensity columns.

There should be some logic checking that these columns are present, and if not we should generate them using fp_calculate_pola_aniso_int() (and this function can then become internal). This must be done after mapping internal column names to the actual names designated by the metadata file, because fp_calculate_pola_aniso_int() relies on these internal names.

Overview of this logic:

• set column names according to metadata files;
• check for polarization, anisotropy and intensity columns;
• if not present, calculate them with fp_calculate_pola_aniso_int().

[Guillawme]

Or, alternative way: ignore pre-calculated polarization, anisotropy and intensity and always recalculate them with fp_calculate_pola_aniso_int(). This would make the metadata file simpler than it is now, as the user would only need to indicate raw data (parallel and perpendicular) column names.