Move snapshot related traits to their proper place (#11012)

* Move snapshot to own crate
Sort out imports

* WIP cargo toml

* Make snapshotting generic over the client
Sort out tests

* Sort out types from blockchain and client

* Sort out sync

* Sort out imports and generics

* Sort out main binary

* Fix sync test-helpers

* Sort out import for secret-store

* Sort out more imports

* Fix easy todos

* cleanup

* Move SnapshotClient and SnapshotWriter to their proper places
Sort out the circular dependency between snapshot and ethcore by moving all snapshot tests to own crate, snapshot-tests

* cleanup

* Cleanup

* fix merge issues

* Update ethcore/snapshot/snapshot-tests/Cargo.toml

Co-Authored-By: Andronik Ordian <write@reusable.software>

* Sort out botched merge

* Ensure snapshot-tests run

* Docs

* Fix grumbles

ethcore/src/client/client.rs

@@ -75,8 +75,6 @@ use client_traits::{
 	Nonce,
 	ProvingBlockChainClient,
 	ScheduleInfo,
-	SnapshotClient,
-	SnapshotWriter,
 	StateClient,
 	StateOrBlock,
 	Tick,
@@ -96,7 +94,7 @@ use machine::{
 	transaction_ext::Transaction,
 };
 use miner::{Miner, MinerService};
-use snapshot;
+use snapshot::{self, SnapshotClient, SnapshotWriter};
 use spec::Spec;
 use state_db::StateDB;
 use trace::{self, Database as TraceDatabase, ImportRequest as TraceImportRequest, LocalizedTrace, TraceDB};