Update go-fil-markets for data transfer IPLD based Vouchers

[hannahhoward]

What

Update the various voucher / voucher result types used in go-data-transfer to work with the proposed updates to the voucher system in filecoin-project/go-data-transfer#305

The current voucher / voucher result types that need to be converted to bindnode are as follows:

• https://github.com/filecoin-project/go-fil-markets/blob/master/retrievalmarket/types.go#L322
• https://github.com/filecoin-project/go-fil-markets/blob/master/retrievalmarket/types.go#L337
• https://github.com/filecoin-project/go-fil-markets/blob/master/retrievalmarket/types.go#L356
• https://github.com/filecoin-project/go-fil-markets/blob/master/storagemarket/impl/requestvalidation/types.go#L48

Most of our code using these vouchers can be found in:

• https://github.com/filecoin-project/go-fil-markets/tree/master/storagemarket/impl/requestvalidation
• https://github.com/filecoin-project/go-fil-markets/tree/master/storagemarket/impl/dtutils
• https://github.com/filecoin-project/go-fil-markets/tree/master/retrievalmarket/impl/requestvalidation
• https://github.com/filecoin-project/go-fil-markets/tree/master/retrievalmarket/impl/dtutils

Landmines

• v0 retrieval types -- we have some additional older versions of the retrieval types which have been forever and have long since stopped being used in any running version of Lotus or filclient. What a great opportunity to delete them!
• retrieval DealProposal type -- probably the biggest landmine is that the DealProposal type has a selector, that is current encoded as a cbg.Deferred. This should definitely become an Any in schema and a datamodel.Node in the node. However, an additional issues is that DealProposal is currently encoded in the client and provider on disk states, which are CBOR-gen types. I'm not exactly sure how to solve this. Two ideas I had are --
  1. Make a seperate copy for the vouchers
  2. Implement the expected cbor-gen methods -- there are only two -- https://github.com/whyrusleeping/cbor-gen/blob/master/utils.go#L130 & https://github.com/whyrusleeping/cbor-gen/blob/master/utils.go#L134 -- using ipld-primes dagcbor methods -- if you do this I think maybe it will serialize / deserialize properly?