Make Ghengin use an unrestricted monad

[alt-romes]

While I think it is a good decision for the core of the engine and the renderer implementations to use the linear IO monad to track resources, I don't think it was a good decision to have that in ghengin, the package bringing it all together with batteries included, for the user.

Instead, the Ghengin monad should wrap the renderer/core monad with UrT (thereby making it an unrestricted monad).
We'd ensure

• The Core implementation and management of linear resources is correct by use of linear types, and brings sanity to the developers and engine developers relying directly on core
• The batteries included ghengin does not enforce linearity everywhere on the users
  • Some functions might still require linear types, that's a good thing: even though not every single thing must be tracked linearly in the monadic binding, certain things might still require linearity
  • We can drop linear-apecs and all those hacks which are just plain wrong really.
  • We'll more clearly manage renderer resources whithin the renderer (and no longer in the apecs store, which was also not a great design decision)
  • I'm still unsure of how exactly to do this split between unrestricted/linear while keeping safety of resources. I think it will come down to exposing just the right amount of linear functions for the things that do need linearity, but I don't think it'll be easy