give a name to the virtualenv

[gerbaudo]

We should give a name to the virtual environment, even if it's use only one environment (i.e. no multiple versions of various packages), and even if the name is something like 'defaultenv'.

Right now we use './', and we end up with several directories that we need to add gitignore. This change requires a few changes in the pathnames used in the scripts here and there.

[gerbaudo]

P.S. when this is done, we should rename 'python/' to 'bin/'. Since most of the code will be in python, it doesn't make sense to have a directory 'python'.