* Add a barebones common crate
* Refactor some code into the common crate
* Add a `ResolverApi` interface.
This commit adds a `ResolverApi` trait to the `format` crate that can be
implemented by any type that can act as a resolver. A resolver is able
to provide information on the chain state. This chain state could be
fresh or it could be cached (which is something that we will do in a
future PR).
This cleans up our crate graph so that `format` is not depending on the
node interactions crate for the `EthereumNode` trait.
* Cleanup the blocking executor
Omar