added pip to make install

As suggested, I added pip to make install.

However, I'm not sure whether this is how we want this. Packages now go to /usr/lib/micropython instead of /.micropython/lib. I'm not fully sure what's going on with the virtualenvs in this script.
Please review thoroughly and bounce in case.

Somehow I also managed to get some commits into this from an earlier experiment that shouldn't be there at all.
Thanks for your patience, I still have a lot to learn.