Best way to use univers to sort and compare Package versions

This relates to work I'm doing for issue #1228.

For the past week or so I've been using several helper functions I created inside the `Package` class, together with a new property function I've added, to compare and sort `Package` versions using [univers ](https://github.com/nexB/univers) version classes -- needed to find the closest greater-than fixed by version and both the closest and the latest non-vulnerable versions.

I now understand that `univers` has built-in mapping that provides a far more straightforward (and no doubt less error-prone ;-) way to accomplish the same goals. I'm currently cleaning up my issue #1228 code (though with much more to do on that issue) so I can push that code and then explore using the built-in `univers` capabilities. If I have any questions related to the process, I'll post them here, and will also share here the results of my `univers` adventure.