Fix gray/incorrect security image after relog

interface/resources/qml/hifi/commerce/wallet/WalletHome.qml

@@ -68,6 +68,7 @@ Item {
     Connections {
         target: GlobalServices
         onMyUsernameChanged: {
+            transactionHistoryModel.clear();
             usernameText.text = Account.username;
         }
     }

interface/src/commerce/Wallet.cpp

@@ -321,6 +321,16 @@ Wallet::Wallet() {
     auto accountManager = DependencyManager::get<AccountManager>();
     connect(accountManager.data(), &AccountManager::usernameChanged, this, [&]() {
         getWalletStatus();
+        _publicKeys.clear();
+
+        if (_securityImage) {
+            delete _securityImage;
+        }
+        _securityImage = nullptr;
+
+        // tell the provider we got nothing
+        updateImageProvider();
+        _passphrase->clear();
     });
 }