Implement native support for Price Oracles.
A Price Oracle is used to bring real-world data, such as market prices,
onto the blockchain, enabling dApps to access and utilize information
that resides outside the blockchain.
Add Price Oracle functionality:
- OracleSet: create or update the Oracle object
- OracleDelete: delete the Oracle object
To support this functionality add:
- New RPC method, `get_aggregate_price`, to calculate aggregate price for a token pair of the specified oracles
- `ltOracle` object
The `ltOracle` object maintains:
- Oracle Owner's account
- Oracle's metadata
- Up to ten token pairs with the scaled price
- The last update time the token pairs were updated
Add Oracle unit-tests
