WIP: Add initial aptly support

This commit integratates aptly backend:

* Creating a new project on OBS, creates aptly repo (using default name
  convention). The repo is automatically published.
* Removing the project on OBS, removes and unpublishes the aptly repo.
* Adding a package on OBS, automatically adds to built packages to the
  aptly repo.
* Removing the package on OBS, removes the built packages from the aptly
  repo.
* Previous versions of a package are automatically removed when an
  updated version is uploaded.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>