Improve QML syntax and update license headers.

app/qml/SimpleSlider.qml

@@ -1,5 +1,5 @@
 /*******************************************************************************
-* Copyright (c) 2013 "Filippo Scognamiglio"
+* Copyright (c) 2013-2021 "Filippo Scognamiglio"
 * https://github.com/Swordfish90/cool-retro-term
 *
 * This file is part of cool-retro-term.
@@ -17,7 +17,6 @@
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *******************************************************************************/
-
 import QtQuick 2.2
 import QtQuick.Controls 2.0
 import QtQuick.Layouts 1.1
@@ -33,12 +32,12 @@ RowLayout {
 
     id: setting_component
     spacing: 10
-    Slider{
+    Slider {
         id: slider
         stepSize: parent.stepSize
         Layout.fillWidth: true
     }
-    SizedLabel{
+    SizedLabel {
         text: Math.round(value * maxMultiplier) + "%"
     }
 }