Improved game provenance tracking

[bmdhacks]

The purpose of this PR is to track external game information about the ports we offer. This includes knowing the steam id, igdb id, and itch.io url for all ports. With this information, scripts are provided to sort external games based on a heuristic "popularity" by blending things like igdb pageviews and steam review numbers.

Here's a description of each file:
port_ids.json - a json file that maps portname to the three external game databases
port_popularity.json - this maps port names to IGDB PopScore heuristics
tools/igdb_popularity.py - this uses IGDB api to convert port_ids.json into port_popularity.json
tools/rank_games_by_popularity.py - an example script to order the games based on a blended popularity heuristic
tools/update_game_ids.py - this adds new games from a port repo into the port_ids.json file, assuming they have v5 json format

[bmdhacks]

Gonna close this for the moment until we figure out what we want in port.json for new ports.