Minting moments with a sub-edition

[jrkhan]

Issue To Be Solved

We will need a way for newly minted Top Shot NFTs to have a subedition. The sub edition is intended to have it's own serial number range. (e.g. if we were to mint 100 moments total, the diamond sub edition will have serials 1-10, the golden sub edition would have serials 1 - 25, the base edition would have serials 1-65, the total edition size would need to be 100)
We will also need a way to store the subedition of each NFT (with all existing moments defaulting to the 'base edition' sub edition).

(Optional): Suggest A Solution

Potential solution for adding to the existing TopShot contract with the bulk of functionality living in a new contract:
https://sketchboard.me/rDsJU4sQGlN

Initial pass at minting sub editions with their own serial range has been added here:
#163

[jrkhan]

The initial pass at this has a second contract which manages the sub edition counts. It will also (as a ledger contract) store the mapping of the moment to the sub edition.