Create trace APIs

[majecty]

The indexer is re-calculating what a node has calculated. The reward calculation of the dynamic validator is also calculated in the indexer, which is very complicated. If CodeChain provides the Trace API, which tells what values in the state are changed for each block, it will help greatly when creating an application

• Go Ethereum's trace API link
• Parity's trace API link

[kseo]

We renamed Trace API to Informer API. See #137.