New Proposal: add meta transaction proposal

[Jim8y]

Based on EIP-712, propose neo's standard meta transaction format.

Major difference:

chainId = > networkId, data = > script.

'''Data Structures''':

• '''Domain''': ** networkId: Integer representing the NEO network identifier. ** version: String representing the version of the meta-transaction format.
• '''Message''': ** nonce: Integer, a unique number ensuring each signature is unique. ** from: String, address of the sender. ** to: String, address of the receiver. ** value: Integer, amount being transferred in smallest unit. ** script: Bytes, script related to the transaction.