Fix tab order after expanding categories or using search

This reimplements the behavior of pressing tab/backtab to force the correct order of items in the listview.

resources/qml/Settings/SettingComboBox.qml

@@ -10,6 +10,7 @@ import UM 1.1 as UM
 SettingItem
 {
     id: base
+    property var focusItem: control
 
     contents: ComboBox
     {
@@ -108,6 +109,15 @@ SettingItem
             }
         }
 
+        Keys.onTabPressed:
+        {
+            base.setActiveFocusToNextSetting(true)
+        }
+        Keys.onBacktabPressed:
+        {
+            base.setActiveFocusToNextSetting(false)
+        }
+
         Binding
         {
             target: control