BasicButton: Make textColor property internal

Change-Id: I1b328bfaa656b1482b9dac73f2ce07a0100fb374
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

src/private/BasicButton.qml

@@ -91,14 +91,11 @@ Control {
         The default value is \c false. */
     property bool activeFocusOnPress: false
 
-    /*! This property holds the button text color.
-
-        The default value is SystemPalette::text. */
-    property color textColor: syspal.text
-
     /*! This property holds the button tooltip. */
     property string tooltip
 
+    /*! \internal */
+    property color __textColor: syspal.text
     /*! \internal */
     property string __position: "only"
     /*! \internal */