Also updates Bulletproofs from C to not be length prefixed, yet rather
have Rust calculate their length.
Corrects an error in key_gen where self was blamed, instead of the
faulty participant.
Updates CLSAG signing as needed. Moves around Error types.
CLSAG multisig and the multisig feature is currently completely borked
because of this. The created TXs are accepted by Monero nodes.