fix(engine): Zones rework

[Jameskmonger]

• revert https://github.com/2004scape/Server/commit/01b398a12a83175a0a600b53b371d693c4035694
• implement objs in Zone (private objs for player and revealed/public objs)

Some still to go, there seems to be a couple of issues (e.g. npcs dont drop items) and a few TODOs

TODO / bugs:

• [x] npc deaths seem broken (hitpoints don't get restored)
• [x] npcs dont drop loot