Clear trackedTokens so that a user starts tracking the new WETH and no longer the old one

packages/website/ts/index.tsx

@@ -10,6 +10,7 @@ import {BrowserRouter as Router, Link, Redirect, Route, Switch} from 'react-rout
 import * as injectTapEventPlugin from 'react-tap-event-plugin';
 import {createStore, Store as ReduxStore} from 'redux';
 import {createLazyComponent} from 'ts/lazy_component';
+import {trackedTokenStorage} from 'ts/local_storage/tracked_token_storage';
 import {tradeHistoryStorage} from 'ts/local_storage/trade_history_storage';
 import {About} from 'ts/pages/about/about';
 import {FAQ} from 'ts/pages/faq/faq';
@@ -29,6 +30,7 @@ BigNumber.config({
 
 // Check if we've introduced an update that requires us to clear the tradeHistory local storage entries
 tradeHistoryStorage.clearIfRequired();
+trackedTokenStorage.clearIfRequired();
 
 const CUSTOM_GREY = 'rgb(39, 39, 39)';
 const CUSTOM_GREEN = 'rgb(102, 222, 117)';

packages/website/ts/local_storage/tracked_token_storage.ts

@@ -1,10 +1,21 @@
 import * as _ from 'lodash';
 import {localStorage} from 'ts/local_storage/local_storage';
 import {Token, TrackedTokensByNetworkId} from 'ts/types';
+import {configs} from 'ts/utils/configs';
 
 const TRACKED_TOKENS_KEY = 'trackedTokens';
+const TRACKED_TOKENS_CLEAR_KEY = 'lastClearTrackedTokensDate';
 
 export const trackedTokenStorage = {
+    // Clear trackedTokens localStorage if we've updated the config variable in an update
+    // that introduced a backward incompatible change requiring the tracked tokens to be re-set
+    clearIfRequired() {
+        const lastClearFillDate = localStorage.getItemIfExists(TRACKED_TOKENS_CLEAR_KEY);
+        if (lastClearFillDate !== configs.lastLocalStorageTrackedTokenClearanceDate) {
+            localStorage.removeItem(TRACKED_TOKENS_KEY);
+        }
+        localStorage.setItem(TRACKED_TOKENS_CLEAR_KEY, configs.lastLocalStorageTrackedTokenClearanceDate);
+    },
     addTrackedTokenToUser(userAddress: string, networkId: number, token: Token) {
         const trackedTokensByUserAddress = this.getTrackedTokensByUserAddress();
         let trackedTokensByNetworkId = trackedTokensByUserAddress[userAddress];

packages/website/ts/utils/configs.ts

@@ -14,6 +14,7 @@ export const configs = {
     // WARNING: ZRX & WETH MUST always be default trackedTokens
     defaultTrackedTokenSymbols: ['WETH', 'ZRX'],
     lastLocalStorageFillClearanceDate: '2017-11-22',
+    lastLocalStorageTrackedTokenClearanceDate: '2017-12-13',
     isMainnetEnabled: true,
     outdatedWrappedEthers: [
         {