Add initial version of games catalog

[edwardchalstrey1]

Issues closed by this PR

• Closes Create initial games catalog from contrib/games #731

Description of the changes in this PR

This PR adds infrastructure and documentation for a first version of the Catalog of games:

• Catalog games can be created by adding NFG/EFG files to catalog dir
• pygambit can load games from outside the pygambit code (in catalog dir)
• Moves several game files from contrib/games to catalog to test catalog functionality
• Updates tutorials to load from catalog
• Adds a page to the docs with all Catalog games, linked to on the docs navbar which just has the game slug and title for now
• Adds a script called src/pygambit/update_catalog.py that you run after adding a new EFG/NFG (usage described in developer docs)
• Also contains change from Fix printing normal form games #757

How to review this PR

• Look at the Catalog of games page
• Review the developer docs page on Updating the Games Catalog
• Take a look at the Loading games from the catalog section added to Tutorial 1

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[edwardchalstrey1]

This is how we get the pygambit.catalog module to be built using code from catalog dir at the root of the repo

[edwardchalstrey1]

This is how the catalog files get included as package data

[edwardchalstrey1]

Also, a question for reviewers:

Will there only ever be a single game file in the catalog for games that can be represented in both normal and extensive form? For example, in contrib/games we have both 2x2x2.nfg and 2x2x2.efg, but should we just have one in the catalog if you can transpose between the two?

If not I would need a type argument for the load function for cases where we have nfg and efg versions of a game pygambit.catalog.load("2x2x2", type="nfg") or perhaps pass in the filename with extension.