Openbazaar python launcher

new pull request after 1st round of reviews.
Thanks @Renelvon this has the merged changes from your repo.

(@Renelvon I kept that REVERT commit you put there as I'm not sure I understood what was right or wrong about it, I figured it'd be easier to fix here now)
The `checkstyle.sh` script isn't automatically invoked during configuration, so no worries.

We could add a warning, however, if it fails to find `pylint`: "Are you executing this from inside the virtualenv?". I believe that's enough hint for the user.