Cleanup QML imports and license headers

- Group the imports into Qt, KDE, NeoChat
- Import the latest versions
- Remove unused imports
- Remove unused components
- Unify license header styling

imports/NeoChat/Dialog/EmojiDialog.qml

@@ -1,11 +1,10 @@
-/**
- * SPDX-FileCopyrightText: 2020 Carl Schwan <carl@carlschwan.eu>
- *
- * SPDX-License-Identifier: LGPL-2.1-or-later
- */
-import QtQuick 2.14
-import QtQuick.Controls 2.14 as QQC2
-import org.kde.kirigami 2.13 as Kirigami
+// SPDX-FileCopyrightText: 2020 Carl Schwan <carl@carlschwan.eu>
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
+import QtQuick 2.15
+import QtQuick.Controls 2.15 as QQC2
+
+import org.kde.kirigami 2.15 as Kirigami
 
 import org.kde.neochat 1.0
 import NeoChat.Component.Emoji 1.0