Add missing license headers, fix some existing

src/monitor/view/MonitorToolButton.qml

+/*
+    SPDX-FileCopyrightText: 2022 Julius Künzel <jk.kdedev@smartlab.uber.space>
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
 import QtQuick 2.11
 import QtQuick.Controls 2.4
 

src/monitor/view/MultiScreenToolBar.qml

+/*
+    SPDX-FileCopyrightText: 2016-2021 Jean-Baptiste Mardelle <jb@kdenlive.org>
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
 import QtQuick.Controls 2.4
 import QtQuick 2.11
 

src/monitor/view/kdenlivemonitortrimming.qml

+/*
+    SPDX-FileCopyrightText: 2021 Julius Künzel <jk.kdedev@smartlab.uber.space>
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
 import QtQuick.Controls 2.4
 import QtQuick.Window 2.2
 import Kdenlive.Controls 1.0

src/timeline2/view/previewmanager.cpp

 /*
     SPDX-FileCopyrightText: 2016 Jean-Baptiste Mardelle <jb@kdenlive.org>
 
-SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
 */
 
 #include "previewmanager.h"

src/timeline2/view/previewmanager.h

 /*
     SPDX-FileCopyrightText: 2016 Jean-Baptiste Mardelle <jb@kdenlive.org>
 
-SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
 */
 
 #ifndef PREVIEWMANAGER_H

src/timeline2/view/qml/SubTitle.qml

+/*
+    SPDX-FileCopyrightText: 2020-2021 Jean-Baptiste Mardelle
+    SPDX-FileCopyrightText: 2020 Sashmita Raghav
+
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
 import QtQuick 2.11
 import QtQuick.Controls 2.4
 

src/timeline2/view/qml/timeline.qml

+/*
+    SPDX-FileCopyrightText: 2017-2021 Jean-Baptiste Mardelle <jb@kdenlive.org>
+    SPDX-FileCopyrightText: 2017 Nicolas Carion
+    SPDX-FileCopyrightText: 2020 Sashmita Raghav
+    SPDX-FileCopyrightText: 2021 Julius Künzel <jk.kdedev@smartlab.uber.space>
+
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
 import QtQuick 2.11
 import QtQml.Models 2.11
 import QtQuick.Controls 2.4

src/timeline2/view/qml/timelineitems.cpp

 /*
-Based on Shotcut, SPDX-FileCopyrightText: 2015-2016 Meltytech LLC
-SPDX-FileCopyrightText: 2019 Jean-Baptiste Mardelle <jb@kdenlive.org>
-This file is part of Kdenlive. See www.kdenlive.org.
+    SPDX-FileCopyrightText: 2015-2016 Meltytech LLC
+    SPDX-FileCopyrightText: 2019 Jean-Baptiste Mardelle <jb@kdenlive.org>
 
-SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+    SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
 */
 
 #include "kdenlivesettings.h"

src/utils/otioconvertions.cpp

 /*
-    this file is part of Kdenlive, the Libre Video Editor by KDE
     SPDX-FileCopyrightText: 2019 Vincent Pinon <vpinon@kde.org>
 
     SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL

src/utils/thememanager.cpp

 /*
-    This file is part of KDevPlatform
     SPDX-FileCopyrightText: 2016 Zhigalin Alexander <alexander@zhigalin.tk>
 
     SPDX-License-Identifier: LGPL-3.0-only OR LicenseRef-KDE-Accepted-LGPL

src/utils/thememanager.h

 /*
-    This file is part of KDevPlatform
     SPDX-FileCopyrightText: 2016 Zhigalin Alexander <alexander@zhigalin.tk>
 
     SPDX-License-Identifier: LGPL-3.0-only OR LicenseRef-KDE-Accepted-LGPL