Remove references to parity-ethereum (#11525)

* update all the changelogs

* update only github URLs in README.md

* sed magic

find . -type f -exec sed -i 's_paritytech/parity-ethereum_OpenEthereum/open-ethereum_g' {} \;

util/network-devp2p/src/node_table.rs

@@ -704,7 +704,7 @@ mod tests {
 		assert_eq!(table.get_index_to_insert(None), 0);
 
 		// sleep 1 mcs is added because nanosecond precision was lost since mac os x high sierra update
-		// https://github.com/paritytech/parity-ethereum/issues/9632
+		// https://github.com/OpenEthereum/open-ethereum/issues/9632
 
 		table.add_node(node1);
 		sleep(Duration::from_micros(1));