Make XP NFT upgradeable

[0x-r4bbit]

Here we need to see if this is really a necessity to make it an upgradeable contract, or if it's enough to allow for configurable dependencies.

[0x-r4bbit]

I've been thinking about this one for a bit.

I think we're good with just having the metadata generator configurable.
This allows for upgrades without users having to take any action an we don't need to introduce a proxy pattern.

If for whatever reason the requirements of the NFT change so drastically that it justifies completely new contract logic, then we can put out a V2 and mint then to existing holders of the v1 token.