Switch aggregate repository package resolution to all feeds for latest instead of just first location found (Vertical)

[ferventcoder]

It's better by default to resolve packages across all feeds and find the latest version of that package no matter the feed priority. Up to this time the package resolution would have been vertical, which means the first feed in priority order that had the package was the one that was used, even if a newer version was found.

This is related to #282 and #279.

[gep13]

Based on discussion with @pauby, this will likely not be included in a 1.0.0 release, but rather a 2.0.0 once we have a baseline of current functionality.