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.

zero-chain/core/proofs/src/transaction.rs

Line 68 in 553e7e0

// TODO: Creating bridge_convert traits between std and no_std.