Disentangle C-chain and X-chain from P-chain

[EricForgy]

In my opinion, separating X-chain and C-chain from P-chain should happen before #14.

As mentioned in this comment: #14 (comment)

If you don't mind me thinking out loud: if the P-chain becomes the "primenet" but still requires X and C to be validated in the same set, these two would, in my opinion, feel "bolted on" for legacy purposes rather than actually being relevant.

It seems to me that implementing #14 would be much cleaner and compelling if C-chain and X-chain were jetisoned as dependencies of P-chain.

How difficult would that be?

PS: Seeing suggestions like this inspired me to bring this up.

PPS: I am currently listening to this and POG mentioned the posibility of having Subnet-only validator just verifying P-chain, but if P-chain were cleanly separated, then they could fully validate.

[Adventuremonkey]

I agree with Disentangling. Here is a more detailed proposal. #88