qml: Add copyright headers to QML files

Github-Pull: bitcoin-core#34
Rebased-From: f82209d

Author: hebasto

src/qml/BitcoinApp/initerrormessage.qml

@@ -1,3 +1,7 @@
+// Copyright (c) 2021-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
 import QtQuick
 import QtQuick.Dialogs
 

src/qml/BitcoinApp/stub.qml

@@ -1,3 +1,7 @@
+// Copyright (c) 2021-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
 import QtQml
 import QtQuick.Controls