Center section label and change it's color

This commit horizontally centers the section label and gives it a
disabled text color, this helps visually separate this label from
the actual messages and makes it easier to scan.

imports/NeoChat/Component/Timeline/SectionDelegate.qml

@@ -9,6 +9,8 @@ import org.kde.kirigami 2.15 as Kirigami
 Kirigami.Heading {
     level: 4
     text: model.showSection ? section : ""
+    color: Kirigami.Theme.disabledTextColor
+    horizontalAlignment: Text.AlignHCenter
     verticalAlignment: Text.AlignVCenter
     topPadding: Kirigami.Units.largeSpacing * 2
     bottomPadding: Kirigami.Units.smallSpacing