Automate making astropy affiliated/openAstro stay in sync

[eteq]

As discussed in this comment of #1, it would be useful to automate the process of keeping OpenAstronomy and the astropy affiliated channel in sync (i.e., should only need to be affiliated to be on OpenAstro).

From @mwcraig :

At the moment the transfer is manual (in the sense that I ran a script locally to do the initial copying). I've been meaning to open a PR to conda-build-all to allow cross-channel copying, but it won't happen for a couple more weeks at least.

It is tempting to move all of the building over here because it has a separate travis/appveyor build queue, but that gets a little complicated for maintaining a separate affiliate channel.

[Cadair]

Can we not just do the channel copy for a given set of packages at the end of each build. It would be nice to do the same for the sunpy channel as well.