Added class based cell_processor as well as 1 test for the module

I added a the cell_processor module which includes the cell processing routines to be used. The module has an improvement in comparison with the previous prototypes:

• Make use of the Babelgrid library to generate the cell geometry based on the quadkey, before the input needed to be a pandas DataFrame, now it only needs quadkey codes.

I also added one test that runs fine in my computer but not in gitlab.

Do I need to fix the .gitlab-ci.yml or the setup.py?

\fyi \rfc \approve @ds @fd