fixes bug 785430 - Add a service to add new products

@rhelmer r?

This basically just does what [the documentation](http://socorro.readthedocs.org/en/latest/installation/add-product-release.html) says to do except it makes it possible to kick this off from the middleware.

Once this has been done and you think it's good, I'll add it to the webapp and its admin UI. 
Why did you put this in a new file and not in ``external/potsgresql/products.py``? You can do that and call your function ``post_releases`` or ``create_releases``, and it will work the same. The original thought was to organize endpoints per resource (here, the products) and then have a function per speciality.