[#534] Use UnifiedSpendingKey for shielding and Spending
This commit implements the use of Unified Spending Keys for shielding
and spending as well as rolling Unified Addresses.
Users should obtain addresses by rolling them from the SDK.
USKs replace Sapling Extended Spending keys and TransparentAccountPrivKeys
when shielding or spending
Closes#534
Co-authored-by: Kris Nuttycombe <kris@nutty.land>
* Fix rebase issues
* PR Suggestion. Make `lastError` an Optional
* Fix test `testReOrgRemovesOutboundTxAndIsNeverMined`
Co-authored-by: Kris Nuttycombe <kris@nutty.land>
7806b5114f