Add some missing PlasmaCore imports

src/declarativeimports/plasmacomponents/qml/TabGroup.qml

@@ -41,6 +41,7 @@
 import QtQuick 2.2
 import "private/TabGroup.js" as Engine
 
+import org.kde.plasma.core 2.0 as PlasmaCore
 import "." 2.0 as PlasmaComponents
 
 /**

src/declarativeimports/plasmacomponents/qml/ToolButton.qml

@@ -22,6 +22,8 @@ import QtQuick 2.1
 import QtQuick.Controls 1.2 as QtControls
 import QtQuick.Controls.Styles.Plasma 2.0 as Styles
 
+import org.kde.plasma.core 2.0 as PlasmaCore
+
 /**
  * A plasma theme based toolbutton.
  *

src/declarativeimports/plasmacomponents/qml/private/TabBarLayout.qml

@@ -58,6 +58,8 @@ import QtQuick 2.1
 import org.kde.kquickcontrolsaddons 2.0
 import "AppManager.js" as Utils
 
+import org.kde.plasma.core 2.0 as PlasmaCore
+
 Item {
     id: root
 

src/declarativeimports/plasmaextracomponents/qml/Heading.qml

@@ -18,8 +18,10 @@
 */
 
 import QtQuick 2.0
+import org.kde.plasma.core 2.0 as PlasmaCore
 import org.kde.plasma.components 2.0
 
+
 /**
  * A heading label used for subsections of texts.
  *