Adding an Executable class and a helper function which following a similar...

See merge request Oriol.Tinto/otils!1

# Conflicts:
#   OTils/file_dealer.py
#   OTils/test/test.py

Adding an Executable class and a helper function which following a similar approach to the one used in spack.

Trying to implement a configuration file to control where we are getting the files from for the file_dealer.