* Rename db_restore => client
* First step: make it compile!
* Second step: working implementation!
* Refactoring
* Fix tests
* PR Grumbles
* PR Grumbles WIP
* Migrate ancient blocks interating backward
* Early return in block migration if snapshot is aborted
* Remove RwLock getter (PR Grumble I)
* Remove dependency on `Client`: only used Traits
* Add test for recovering aborted snapshot recovery
* Add test for migrating old blocks
* Fix build
* PR Grumble I
* PR Grumble II
* PR Grumble III
* PR Grumble IV
* PR Grumble V
* PR Grumble VI
* Fix one test
* Fix test
* PR Grumble
* PR Grumbles
* PR Grumbles II
* Fix tests
* Release RwLock earlier
* Revert Cargo.lock
* Update _update ancient block_ logic: set local in `commit`
* Update typo in ethcore/src/snapshot/service.rs
Co-Authored-By: ngotchac <ngotchac@gmail.com>