Use devpi, drop calgDeps

As it says on the tin. We could follow some other DA projects and just install packages in an almost normal way with mirror instead of building and tagging our own wheels all the time. As posixshmem is not published on pypi, I'd just use proxy for now and eventually maybe replace it with the similar thing found in recent multiprocessing (IIRC, there's slight difference in behavior on opening / closing, will have to check exception handling).