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)
Since there is a brand-new `usage` message, I don't mind breaking backwards compatibility that much. And since there is now a way to install a config file, the patching shouldn't be hard.