wxRibbonButtonBarButton: Implemented mutable lables and minimum label width

Added new function SetButtonText() which modifies labels of
existing ribbon button bar buttons.
The new function SetButtonTextMinWidth() is used to specify the
label width in advance so that lables can be changed without
recalculating the layout.
wxRibbonArtProvider is modified to support these operation.

interface/wx/ribbon/buttonbar.h

@@ -503,6 +503,71 @@ public:
                 const wxBitmap& bitmap_disabled = wxNullBitmap,
                 const wxBitmap& bitmap_small_disabled = wxNullBitmap);
 
+    /**
+        Changes the label text of an existing button.
+
+        @param button_id
+            ID of the button to manipulate.
+        @param label
+            New label of the button.
+
+        @remarks
+            If text size has changed, Realize() must be called
+            on the top level wxRibbonBar object to recalculate panel sizes.
+            Use SetButtonTextMinWidth() to avoid calling Realize()
+            after every change.
+
+        @see SetButtonTextMinWidth
+    */
+    virtual void SetButtonText(int button_id, const wxString& label);
+
+    /**
+        Sets the minimum width of the button label, to indicate to
+        the wxRibbonArtProvider layout mechanism that this is the
+        minimum required size.
+
+        You have to call Realize() after calling this function to
+        apply the given minimum width.
+
+        @param button_id
+            ID of the button to manipulate.
+        @param min_width_medium
+            Requested minimum width of the button text in pixel
+            if the button is medium size.
+        @param min_width_medium
+            Requested minimum width of the button text in pixel
+            if the button is large size.
+
+        @remarks
+            This function is used together with SetButtonText() to change
+            button labels on the fly without modifying the button bar layout.
+
+        @see SetButtonText()
+    */
+    virtual void SetButtonTextMinWidth(int button_id,
+                int min_width_medium, int min_width_large);
+
+    /**
+        Sets the minimum width of the button label, to indicate to
+        the wxRibbonArtProvider layout mechanism that this is the
+        minimum required size.
+
+        You have to call Realize() after calling this function to
+        apply the given minimum width.
+
+        @param button_id
+            ID of the button to manipulate.
+        @param label
+            The minimum width is set to the width of this label.
+
+        @remarks
+            This function is used together with SetButtonText() to change
+            button labels on the fly without modifying the button bar layout.
+
+        @see SetButtonText()
+    */
+    virtual void SetButtonTextMinWidth(int button_id, const wxString& label);
+
     /**
         Returns the active item of the button bar or NULL if there is none.
         The active button is the one being clicked.