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)
Redundant. `checkstyle.sh` should be run from inside the `virtualenv` or else strange things happen. For example, on my machine, if I run `pylint` from outside, it thinks it is running on Python 3 and reports all kinds of "syntax errors". Also, since we are installing a lot of `pip` packages inside the virtualenv, running `pylint` from outside the `virtualenv` will trigger an error once #665 is merged.