Smarter Tokens fetching (#3546)

* Don't auto-subscribe for contracts #3240

* Smarter Balance : don't re-instantiate contracts, fetch tokens #3240

* Smarter Balance Tokens fetching (update image when needed) #3240

* Attaching to TokenReg Events instead of fetching for each block #3240

* Unsubscribe from shapeshit... #3240

* Unsubscribe from EthFilter if used once (resolved) #3240

* Remove warning

* PR review fix

* Typo

* Better contract JS API : one subscribe for all #3546

* Fixed test

js/src/api/util/format.js

@@ -29,3 +29,7 @@ export function hex2Ascii (_hex) {
 
   return str;
 }
+
+export function asciiToHex (string) {
+  return '0x' + string.split('').map((s) => s.charCodeAt(0).toString(16)).join('');
+}