Introduce two variables `Aviso_DT_dir` and `Eurec4A_NRT_dir` to
replace the single variable `large_input_dir`. This should remove the
need to create symbolic links to the files in these directories.

Dictionary instead of list, following update of `test_compare.py`.

Add arguments `input_segments` and `output_segments`. Because on
one occasion I wanted to use and keep two versions of input and output
graphs in the same directory