Use images from all public projects and filter deprecated ones

This is just a proposal. I still haven't run the live tests, as I want some feedback before.

This change removes the hardcoded *debian-cloud* and *centos-cloud* projects as the only sources of images, and moves that to a property users can override. I've added to that property all projects that seem to be public (at least the ones where the images I see in the console belong).

It also adds a property to control whether jclouds should return the deprecated images or not, to make it easier for users to pick the right images. Both properties have the corresponding defaults in the api metadata.

@danbroudy @adriancole WDYT?