Add missing license headers

I'm the sole author of these files

app/qml/MprisSlider.qml

+/**
+ * SPDX-FileCopyrightText: 2019 Nicolas Fella <nicolas.fella@gmx.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
 import QtQuick 2.2
 import QtQuick.Controls 2.2
 

plugins/findthisdevice/kdeconnect_findthisdevice_config.qml

+/**
+ * SPDX-FileCopyrightText: 2019 Nicolas Fella <nicolas.fella@gmx.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
 import QtQuick 2.2
 import QtQuick.Controls 2.2
 import QtQuick.Layouts 1.1

plugins/pausemusic/kdeconnect_pausemusic_config.qml

+/**
+ * SPDX-FileCopyrightText: 2019 Nicolas Fella <nicolas.fella@gmx.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
 import QtQuick 2.2
 import QtQuick.Controls 2.2
 import QtQuick.Layouts 1.1

plugins/runcommand/kdeconnect_runcommand_config.qml

+/**
+ * SPDX-FileCopyrightText: 2019 Nicolas Fella <nicolas.fella@gmx.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
 import QtQuick 2.2
 import QtQuick.Controls 2.5
 import org.kde.kirigami 2.4 as Kirigami

plugins/sendnotifications/kdeconnect_sendnotifications_config.qml

+/**
+ * SPDX-FileCopyrightText: 2019 Nicolas Fella <nicolas.fella@gmx.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
 import QtQuick 2.2
 import QtQuick.Controls 2.2
 import QtQuick.Layouts 1.1

plugins/share/kdeconnect_share_config.qml

+/**
+ * SPDX-FileCopyrightText: 2019 Nicolas Fella <nicolas.fella@gmx.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
 import QtQuick 2.2
 import QtQuick.Controls 2.2
 import QtQuick.Layouts 1.1