Add support for rewards-v3

[vihu]

Summary

Add support for rewards_v3 transaction.

Notes

• rewards_v3 transaction only rewards for consensus, securities and the remaining rewards go to a single treasury
• Ensures all reward related chain vars are gathered once, this significantly simplifies rewards txn
• Adds a basic test and checks whether the rewards are in within some (10 ^ -10) threshold of acceptance
• Metadata for rewards is still exported along with some other potentially useful functions (get_reward_vars/3 for example)

TODO

• [ ] Check whether aux ledger still works

[Vagabond]

Seems reasonable