feat: verify (always) Amount matches Commitment

[dan-da]

High level changes:

1. The check that secret amount matches commitment is now moved inside Dbc::verify() so there is no chance of a wallet forgetting to do it.

2. We standardize on verify/verification instead of validate/validation. This matches usage in ringct and blsttc, so it makes the api more regular.

Details:

• change validate command to verify in mint-repl
• impl From instead of Into
• impl From instead of Into
• replace validate/validation with verify/verification in code/comments
• rename validation.rs to verification.rs
• rename TransactionValidator to TransactionVerifier
• rename Dbc::confirm_valid() to verify()
• verify that secret Amount matches public Commitment inside Dbc::verify()
• update tests appropriately