develop branch - Multiple indentation errors

[mdpoleto]

Hi,

I have cloned the repo and switched to the develop branch in order to use Python3. However, I get multiple indentation errors in atoms_to_morph.py (I haven't check the other files yet). It seems there is a mix of tabs and spaces in the file and that is raising errors. I tried to replace "\t" with 8 spaces (it seems to be the case here) but even that failed on lines like 329, for instance, in which you have an odd number of spaces.

I am not sure that is a known issue but I just wanted to let you known.
Thanks!