ui: show the name of the account being migrated

When multiple accounts need to be migrated, it's better to know
which one is being processed when chosing a password.

Change-Id: I29703b48e6892e97bc096f7f8ad4199eacb90a8f

wizarddialog.cpp

@@ -57,7 +57,8 @@ WizardDialog::WizardDialog(WizardMode wizardMode, Account* toBeMigrated, QWidget
 
     if (wizardMode_ == MIGRATION) {
         ui->stackedWidget->setCurrentIndex(1);
-        ui->usernameEdit->hide();
+        ui->usernameEdit->setEnabled(false);
+        ui->usernameEdit->setText(toBeMigrated->displayName());
         ui->previousButton->hide();
         ui->avatarButton->hide();
         ui->pinEdit->hide();