We also add a `type` field to the output objects (matching the field in
`z_viewtransaction`), now that the output type can't be distinguished
solely from the address encoding.
The ZTXOSelector type allows selection of previous Zcash
transaction outputs (both transparent outputs and shielded notes)
on the basis of either a (legacy) bare address, or for a
BIP-44 account.
This adds a new `AddrSet` type for use in note retrieval
as a filter, in place of a heterogeneous list of `RawAddress`
values. `RawAddress` will complicate the handling of addresses
within the wallet after the addition of unified addresses,
because it does not contain transparent receiver types, and
if we retain this polymorphism it means a lot of invalid states
are represented in places we don't want them to be. It's better
to figure out what types of addresses we're working with as soon
as possible after parsing, and use monomorphic calls from there
on in.