Add accountCounter method for blockchain prototype

src/blockchain/accountCounter.js

@@ -0,0 +1,27 @@
+const iteratorStream = require('async-iterator-to-stream');
+const api = require('../helper');
+const { sleep } = require('../utils');
+
+/**
+ * Stream account counter
+ * @returns {Stream.<Number>} - account number
+ * @memberof Scan.blockchain
+ */
+function accountCounter() {
+  let latestCatch;
+  const iterator = async function * (ms = 700) {
+    while (true) {
+      const count = await api.getAccountCount();
+      if (count && latestCatch !== count) {
+        latestCatch = count;
+        yield count;
+      }
+
+      await sleep(ms);
+    }
+  };
+
+  return iteratorStream.obj(iterator());
+}
+
+module.exports = accountCounter;