Move Externalities into its own crate (#3775)

* Move `Externalities` into `substrate-externalities`

- `Externalities` now support generic extensions
- Split of `primtives-storage` for storage primitive types

* Move the externalities scoping into `substrate-externalities`

* Fix compilation

* Review feedback

* Adds macro for declaring extensions

* Fix benchmarks

* Introduce `ExtensionStore` trait

* Last review comments

* Implement it for `ExtensionStore`

substrate/srml/support/test/tests/instance.rs

@@ -15,20 +15,22 @@
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 #![recursion_limit="128"]
 
-use runtime_io::with_externalities;
+use sr_primitives::{
+	generic, BuildStorage, traits::{BlakeTwo256, Block as _, Verify},
+	set_and_run_with_externalities,
+};
 use support::{
 	Parameter, traits::Get, parameter_types,
-	sr_primitives::{generic, BuildStorage, traits::{BlakeTwo256, Block as _, Verify}},
 	metadata::{
 		DecodeDifferent, StorageMetadata, StorageEntryModifier, StorageEntryType, DefaultByteGetter,
-		StorageEntryMetadata, StorageHasher
+		StorageEntryMetadata, StorageHasher,
 	},
 	StorageValue, StorageMap, StorageLinkedMap, StorageDoubleMap,
 };
 use inherents::{
 	ProvideInherent, InherentData, InherentIdentifier, RuntimeString, MakeFatalError
 };
-use primitives::{H256, sr25519, Blake2Hasher};
+use primitives::{H256, sr25519};
 
 mod system;
 
@@ -275,7 +277,7 @@ pub type Header = generic::Header<BlockNumber, BlakeTwo256>;
 pub type Block = generic::Block<Header, UncheckedExtrinsic>;
 pub type UncheckedExtrinsic = generic::UncheckedExtrinsic<u32, Call, Signature, ()>;
 
-fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
+fn new_test_ext() -> runtime_io::TestExternalities {
 	GenesisConfig{
 		module1_Instance1: Some(module1::GenesisConfig {
 			value: 3,
@@ -329,7 +331,7 @@ fn storage_instance_independance() {
 
 #[test]
 fn storage_with_instance_basic_operation() {
-	with_externalities(&mut new_test_ext(), || {
+	set_and_run_with_externalities(&mut new_test_ext(), || {
 		type Value = module2::Value<Runtime, module2::Instance1>;
 		type Map = module2::Map<module2::Instance1>;
 		type LinkedMap = module2::LinkedMap<module2::Instance1>;