zebra-state can't be used to implement light wallets, because it keeps a
copy of the chain state.
Document this design choice in the design doc.
Closes#425.
* rename zebra-storage to zebra-state
* Setup initial skeleton for zebra-state
* add test
* Apply suggestions from code review
Co-authored-by: Henry de Valence <hdevalence@hdevalence.ca>
* move shared test vectors to a common crate
Co-authored-by: Jane Lusby <jane@zfnd.org>
Co-authored-by: Henry de Valence <hdevalence@hdevalence.ca>