Ramon co pet (#73)

* GIES and AVO Smeaheia in progress

* avo updted, grav included, method for joint grav and avo. calc_pem method in flow_rock that is read by flow_avo

* softsand.py represents soft sand rock physics model, added 4D gravity and 4D avo

* give overburden velocity values to inactive cells

* minor edits

---------

Co-authored-by: Martha Økland Lien <mlie@bgo-1907.ad.norceresearch.no>
Co-authored-by: Rolf J. Lorentzen <rolo@norceresearch.no>

Author: 3 people

setup.py

@@ -45,5 +45,6 @@
         'libecalc',
         'scikit-learn',
         'pylops'
+
     ] + EXTRAS['doc'],
 )