GZAP: Key tracking refactor

[ToxicFrog]

This is a blanket issue for the key management subsystem redesign planned for 0.4.4/0.5.0. It should fix issues with Adventures of Square (and other wads that rely on enemies that drop keys, or keys that spawn in during gameplay more generally and are thus invisible at scan time), and also lays some groundwork for supporting games with hub-wide keys like Faithless.

• [x] Store keys in the global state rather than individual Region objects
• [x] Support keys scoped to multiple regions
• [ ] Support AP-KEY message to manually set key scope
• [x] Automatically emit AP-KEY message for keys with -INTERHUBSTRIP or if the map being scanned is part of a hubcluster
• [ ] Pass through key region data in the generated pk3
• [x] Automatically create a key tracking structure for new keys found during gameplay (with hubcluster/global key support as above)
• [ ] Emit AP-KEY messages in the tuning file for keys found during gameplay
• [X] Allow key toggling through the inventory menu