Design the key schedule with viewing keys/note encryption

[vveiln]

Design the key schedule with viewing keys/note encryption

[XuyangSong]

The nullifier key commitment has a useless zero (nk_cm = Com(nk, zero)). We could use the space for key management. Or we could put the nullifier key in the new key management design.

Could we merge all the user-related info (nk, other key stuff, and the app_data_dynamic) in the circuit and then put the result in the note commitment? That would prevent lots of bit-wise encoding/decoding in SinsemillaCommit(note commitment). For example, I use the address = hash(nk_cm, app_data_dynamic), although the address naming is inaccurate and will be improved. #123