This change makes the StateDB track the state key value diff of a block transition.
We already tracked current account and storage values for the purpose of updating
the state snapshot. With this PR, we now also track the original (pre-transition) values
of accounts and storage slots.
* trie: add node type common package
In trie/types package, a few node wrappers are defined, which will be used
in both trie package, trie/snap package, etc. Therefore, a standalone common
package is created to put these stuffs.
* trie: rename trie/types to trie/trienode
