Theme consistency overhaul:

- Add surface shift option, start from surface by default (previously
  was surfaceContainer). Old colors can be attained by changing it back
to "container" in theme colors
- Remove borders on surface elements, mostly
- Fix popup distances
- Use surfaceContainer/sch by default on widgets

Modules/ControlCenter/Components/HeaderPane.qml

@@ -15,13 +15,10 @@ Rectangle {
 
     implicitHeight: 70
     radius: Theme.cornerRadius
-    color: Qt.rgba(Theme.surfaceVariant.r,
-                   Theme.surfaceVariant.g,
-                   Theme.surfaceVariant.b,
-                   Theme.getContentBackgroundAlpha() * 0.4)
+    color: Theme.surfaceContainerHigh
     border.color: Qt.rgba(Theme.outline.r, Theme.outline.g,
                           Theme.outline.b, 0.08)
-    border.width: 1
+    border.width: 0
 
     Row {
         anchors.left: parent.left