Add `TryFrom` traits to convert original types to zerochain primitive types

[osuketh]

Add TryFrom traits to convert original types to zerochain primitive types in proofs crate. Use Bls12 type instead of JubjubEngine trait in original types in order to avoid recursive definitions.

https://github.com/LayerXcom/zero-chain/blob/553e7e0f0b386964d22ff074126aa78367477bec/core/proofs/src/transaction.rs#L68