Retrieve block headers only for header-only info (#5480)

* Add parity_getBlockHeaderByNumber

* Use parity_getBlockHeaderByNumber for retrieval

js/src/dapps/registry/Events/actions.js

@@ -43,7 +43,7 @@ export const subscribe = (name, from = 0, to = 'pending') =>
 
         events.forEach((e) => {
           Promise.all([
-            api.eth.getBlockByNumber(e.blockNumber),
+            api.parity.getBlockHeaderByNumber(e.blockNumber),
             api.eth.getTransactionByHash(e.transactionHash)
           ])
           .then(([block, tx]) => {

js/src/dapps/signaturereg/services.js

@@ -158,7 +158,7 @@ export function attachEvents (contract, callback) {
 }
 
 export function getBlock (blockNumber) {
-  return api.eth.getBlockByNumber(blockNumber);
+  return api.parity.getBlockHeaderByNumber(blockNumber);
 }
 
 export function callRegister (instance, id, options = {}) {

js/src/dapps/tokendeploy/Deploy/Event/event.js

@@ -94,7 +94,7 @@ export default class Event extends Component {
 
     Promise
       .all([
-        api.eth.getBlockByNumber(event.blockNumber),
+        api.parity.getBlockHeaderByNumber(event.blockNumber),
         getCoin(event.params.tokenreg, event.params.coin)
       ])
       .then(([block, coin]) => {

js/src/dapps/tokendeploy/Transfer/Event/event.js

@@ -97,8 +97,8 @@ export default class Event extends Component {
       return;
     }
 
-    api.eth
-      .getBlockByNumber(event.blockNumber)
+    api.parity
+      .getBlockHeaderByNumber(event.blockNumber)
       .then((block) => {
         this.setState({ block });
       });