EnumerableStorageMap (#1763)

* Refactor decl_storage a bit to allow easier impl of linked map.

* A bunch of refactorings for storage generation.

- Rename StorageMap and ChildrenStorageMap to avoid confusion with generator::StorageMap.
- Separate implementation from the procedural macro code to clean it up.
- Make sure that genesis is initialised using the `StorageValue/StorageMap`
  generated implementations instead of going RAW.

* WiP: Writing test.

* Basic implementation.

* Implement enumeration.

* Fix non-std issues.

* fix warning

* Fix test-client.

* Address review grumbles - part 1

* Avoid cloning the key, relax Storage requirements.

* Rebuild runtime.

* Remove dangling todo.

substrate/core/service/src/chain_spec.rs

@@ -21,7 +21,7 @@ use std::fs::File;
 use std::path::PathBuf;
 use serde_derive::{Serialize, Deserialize};
 use primitives::storage::{StorageKey, StorageData};
-use runtime_primitives::{BuildStorage, StorageMap, ChildrenStorageMap};
+use runtime_primitives::{BuildStorage, StorageOverlay, ChildrenStorageOverlay};
 use serde_json as json;
 use crate::components::RuntimeGenesis;
 use network::Multiaddr;
@@ -65,7 +65,7 @@ impl<G: RuntimeGenesis> GenesisSource<G> {
 }
 
 impl<'a, G: RuntimeGenesis> BuildStorage for &'a ChainSpec<G> {
-	fn build_storage(self) -> Result<(StorageMap, ChildrenStorageMap), String> {
+	fn build_storage(self) -> Result<(StorageOverlay, ChildrenStorageOverlay), String> {
 		match self.genesis.resolve()? {
 			Genesis::Runtime(gc) => gc.build_storage(),
 			Genesis::Raw(map) => Ok((map.into_iter().map(|(k, v)| (k.0, v.0)).collect(), Default::default())),