Game configuration: support presets

Some games have well-known presets that can be mapped to varying preconfigured list of item priorities; e.g.:

• Super Metroid: Doors (most beams may be "high")
• LttP: Keysanity (most keys may be "high")

Support presets of item priorities at the game-level; adjust priorities for items that are strictly necessary ("high") given the game's supported settings.

Possible implementation follow-ups to apply a preset:

• Maintenance-module task at the time of world data generation
• Bot command to allow a player to apply a preset on-demand
• Bot command with the ability to upload and apply a custom JSON file (see #58)