This commit replaces the deep-copy based state revert mechanism with a
linear complexity journal. This commit also hides several internal
StateDB methods to limit the number of ways in which calling code can
use the journal incorrectly.
As usual consultation and bug fixes to the initial implementation were
provided by @karalabe, @obscuren and @Arachnid. Thank you!
(cherry picked from commit 1f1ea18b5414bea22332bb4fce53cc95b5c6a07d)
This change introduces a global, per-state cache that keeps account data
in the canon state. Thanks to @karalabe for lots of fixes.
(cherry picked from commit a59a93f476434f2805c8fd3e10bf1b2f579b078f)
