This PR adds the new Blockchain API added to node.
It also makes use of the blockchain API. For code to become clearer, a superclass from NodeAndExplorerDataSourceImpl is extracted: NodeDataSourceImpl. This one only uses node as data source, while NodeAndExplorerDataSourceImpl can fall back to explorer API when needed.
This PR adds the new Blockchain API added to node.
It also makes use of the blockchain API. For code to become clearer, a superclass from NodeAndExplorerDataSourceImpl is extracted: NodeDataSourceImpl. This one only uses node as data source, while NodeAndExplorerDataSourceImpl can fall back to explorer API when needed.