Fix import issues with python

[LucasCampos]

When trying to run the code locally using python, seems like some imports are broken:

(base) ➜  py_vb_toolbox git:(master) ✗ python vb_toolbox/app.py
Traceback (most recent call last):
  File "vb_toolbox/app.py", line 14, in <module>
    import vb_toolbox.io as io
ModuleNotFoundError: No module named 'vb_toolbox'

Seems to work fine when using ipython, though.

(base) ➜  py_vb_toolbox git:(master) ✗ ipython -- vb_toolbox/app.py
usage: app.py [-h] [-j N] [-n norm] [-fb] [-m file] [-c file] -s file -d file
              -o file
app.py: error: the following arguments are required: -s/--surface, -d/--data, -o/--output

This issue happens both with the CLI and the GUI versions of VB_Toolbox.