feat: dusking DBCs, massive renamings

[grumbach]

BREAKING CHANGE: many types renamed

• SNT: the unit of our currency
• Nano: (currently Token) 10^-9 SNT
• CashNote: (currently DBC), spendable unique key along with spend related information, containing n nanos. This CashNote contains unique key related information, leaking it damages privacy but it cannot be spent by an attacker since it doesn’t contain your private key.
• Spend/SignedSpend: Network representation of a spent CashNote, it cannot be linked back to your MainKey. It makes the system auditable and transactions verifiable
• Transaction: (currently DbcTransaction), Network operation that creates new CashNote while spending CashNote of the same total value, transaction information is findable both in CashNotes and in the Spends on the Network.
• NoteRedemption: (currently UTXO) minimal information from which the recipient of a Transaction can redeem their new spendable CashNote
• Transfer: encrypted NoteRedemptions ready to be sent to a transaction recipient so they can receive money.
  As for keys:
• MainSecretKey: (current MainKey) the private main key (secret)
• DerivedSecretKey: (current DerivedKey) a derived key from the main key (IS UNIQUE but secret)
• MainPubkey: (current PublicAddress) the public key of the main key
• UniquePubkey: (current dbc_id) the public key of the derived key (IS UNIQUE)

[grumbach]

Dusking DBCs in safe_network directly. Now this sn_dbc code will be moved to safe_network