[BIP] Normalized transaction IDs

The proposal involved computing the normalized transaction ID and adding it to the UTXO when storing the coin state. However, the proposal was not a complete solution to the problem of malleability and Decker suggested including flags in the UTXO-creating transaction to specify which parts of the signature would be covered. This would allow for fully malleability-proof wallets. Additionally, there was discussion around how to refactor common functionality into reusable blocks and how to annotate incoming transactions with their normalized inputs. Luke also noted that non-VERIFY is not possible as a softfork without doing a second/new P2SH since it can be negated.