Replace error-chain for client error (#2231)

* WIP: convert client error

* Remove error_chain for client error

* Ignore tx-pool error deprecation warning

* Update Cargo.lock files

* Fix tests

* Increment impl_version

* Derive From impls, remove allow(missing_docs)

* Remove space

* Remove redundant into()s

* Blockchain Error source

* Bump impl version

substrate/core/client/src/children.rs

@@ -32,7 +32,7 @@ pub fn read_children<
 
 	let raw_val_opt = match db.get(column, &buf[..]) {
 		Ok(raw_val_opt) => raw_val_opt,
-		Err(_) => return Err(error::ErrorKind::Backend("Error reading value from database".into()).into()),
+		Err(_) => return Err(error::Error::Backend("Error reading value from database".into())),
 	};
 
 	let raw_val = match raw_val_opt {
@@ -42,7 +42,7 @@ pub fn read_children<
 
 	let children: Vec<V> = match Decode::decode(&mut &raw_val[..]) {
 		Some(children) => children,
-		None => return Err(error::ErrorKind::Backend("Error decoding children".into()).into()),
+		None => return Err(error::Error::Backend("Error decoding children".into())),
 	};
 
 	Ok(children)
@@ -118,4 +118,4 @@ mod tests {
 		assert_eq!(r1, vec![1_3, 1_5]);
 		assert_eq!(r2.len(), 0);		
 	}
-}
+}