Price tracker contract for average sales prices for collections (initially only supports Legions)

[treasure-t1dev]

Price tracker is a contract who's sole purpose initially is to track Legion genesis common/uncommon/rare average sales price (requested by Defrag)

TreasureMarketplace changes:

• Added setPriceTracker function guarded by AccessControl to set the address of the price tracker contract to be invoked
• when buying an item, invoke recordSales with the sales information

TreasureNFTPricingTracker:

• initialize with treasure marketplace contract/legion contract/legion metadata contract
• recordSales can only be invoked by the treasure marketplace contract
• recordSales kicks out if the sale isn't a Legion, if the Legion isn't a genesis, or if the Legion isn't common/uncommon/rare
• recordSales currently only saves Legion Genesis sales into 3 different tracked buckets (common, uncommon, rare)
• recordSales emits an AveragePriceUpdated event when a new average is calculated and stored.