Add purchase metadata

[rynoV]

Addresses #8

• Need to confirm about policyId and mintPolicy, unclear how these should be filled
  • policyId is supposed to have a MintingPolicyHash for the collection nft currency symbol, not sure how to get that since we only have the currency symbol
    • Nevermind, a currency symbol is a policy hash and serialization-lib can be used to convert the bytes to ScriptHash
  • mintPolicy is just an arbitrary version string, maybe it's okay to have it empty for now
• Need to confirm which ownerPkh (and ownerPrice) go in the metadata: the value for the input token or the output token
  • Given that the minting transaction would need to include the output token's information, and the updated owner would be required for the output token to be used at all, the value for the output token seems like the correct choice
• Need to use changes from Move Metadata code from CTL #7 and import metadata code from updated location
• Use updated public api currencysymbol in metadata code (need to update CTL to a point which includes these changes)
  • I'm currently converting from Contract.Value.CurrencySymbol to Cardano.Types.Value.CurrencySymbol because of a discrepancy between the metadata and the NftCollection types, maybe the metadata code can be converted to use the Contract.Value.CurrencySymbol (since I believe that is the "public api" and best practice)
• I'll probably also extract the metadata-adding to its own function
• The build is currently broken because of a bug in the build system
  • Using calum/metadata-invalid-char-fix branch of CTL
• Need to test once buy contract is fixed

[samuelWilliams99]

First 2 points - yes
3rd point - Use the one that works for now, but ask in the #ctl channel about whether an issue should be created.

[rynoV]

#22 includes all the changes of this PR (this metadata was necessary for minting too)