Add a simple way to score projects 

While looking at the project suggestions, a ton of the projects were super dead. Sure, they had open issues but they didn't have any recent issues or commits. If I open a PR up against them, it's really likely it'd never get merged. That makes me :sob:.

This is a simple class that would allow us to score projects. Right now, it's all completely dynamic. In a follow-up PR (if this one is well received), I'd like to store the score on the actual `Project` record, update it on a somewhat regular basis, and then update the sorting to consider the scoring. :sparkles: 

cc @andrew since we were chatting about this a fair bit in chat :rabbit: