create MAR utilities in himatpy

This PR adds the new scripts @liuzheng-arctic developed directly into himatpy:

what was formerly "MAR_download.py" is now incorporated as a function in utils.py
I merged all the changes to pygrace.py for now, without testing. We should test these soon
this also includes a .gitignore file and ports over the himat.yml and setup.py file from the HMA repo

aaarendt / HMA_Validation