Small UI fixes (#3966)

* Load dapp visibility from localStorage

* Align MethodDecoding address svg properly

* Consolidate svg & img classes overrides

* improve isNullAddress check

* readOnly for null display

* disabled || readOnly

js/src/util/constants.js

@@ -19,8 +19,11 @@ const DEFAULT_GASPRICE = '20000000000';
 
 const MAX_GAS_ESTIMATION = '50000000';
 
+const NULL_ADDRESS = '0000000000000000000000000000000000000000';
+
 export {
   DEFAULT_GAS,
   DEFAULT_GASPRICE,
-  MAX_GAS_ESTIMATION
+  MAX_GAS_ESTIMATION,
+  NULL_ADDRESS
 };

js/src/util/validation.js

@@ -18,6 +18,8 @@ import BigNumber from 'bignumber.js';
 
 import util from '~/api/util';
 
+import { NULL_ADDRESS } from './constants';
+
 export const ERRORS = {
   invalidAddress: 'address is an invalid network address',
   invalidAmount: 'the supplied amount should be a valid positive number',
@@ -174,3 +176,11 @@ export function validateUint (value) {
     valueError
   };
 }
+
+export function isNullAddress (address) {
+  if (address && address.substr(0, 2) === '0x') {
+    return isNullAddress(address.substr(2));
+  }
+
+  return address === NULL_ADDRESS;
+}