Stronger typo-guarding through metatable errors

[autonordev]

As much as possible, but especially for our main singletons (Cmdr, CmdrClient, Registry, etc) we should use metatables to guard against typos. In other words, we should ensure that we're raising errors whenever developers try to access something that doesn't exist from Cmdr. This will help developers to spot errors immediately and clearly, reducing support requests. I have a mental image of how this should work so I'll try add this when I get a minute.