Statediff for full node (#6)

* Open a trie from the in-memory database

* Use a node's LeafKey as an identifier instead of the address

It was proving difficult to find look the address up from a given path
with a full node (sometimes the value wouldn't exist in the disk db).
So, instead, for now we are using the node's LeafKey with is a Keccak256
hash of the address, so if we know the address we can figure out which
LeafKey it matches up to.

* Make sure that statediff has been processed before pruning

* Use blockchain stateCache.OpenTrie for storage diffs

* Clean up log lines and remove unnecessary fields from builder

* Apply go fmt changes

* Add a sleep to the blockchain test

* Address PR comments

* Address PR comments

eth/config.go

@@ -158,4 +158,6 @@ type Config struct {
 
 	// CheckpointOracle is the configuration for checkpoint oracle.
 	CheckpointOracle *params.CheckpointOracleConfig `toml:",omitempty"`
+
+	StateDiff bool
 }