Define and use the UIHandle and TrackPanelCell protocols, but...

...no actions reimplemented to them yet.

Later commits will move special cases one at a time from TrackPanel, preserving
all click and drag capabilities at each step.  With a few exceptions, but those
lost abilities are restored in yet later commits.  (Ctrl+Click on the Label
track being one.)

src/RefreshCode.h

@@ -0,0 +1,40 @@
+/**********************************************************************
+
+Audacity: A Digital Audio Editor
+
+RefreshCode.h
+
+Paul Licameli
+
+**********************************************************************/
+
+#ifndef __AUDACITY_REFRESH_CODE__
+#define __AUDACITY_REFRESH_CODE__
+
+namespace RefreshCode
+{
+
+   // Bit flags for composing a result that directs the
+   // framework whether to continue, and what to redraw
+   enum {
+      RefreshNone = 0,
+
+      Cancelled = 0x1,
+      RefreshCell = 0x2,        // Refresh the cell passed to Click()
+      RefreshLatestCell = 0x4,  // Refresh the cell passed to latest call
+      RefreshAll = 0x8,
+      FixScrollbars = 0x10,
+      Resize = 0x20,
+      UpdateSelection = 0x40,
+      UpdateVRuler = 0x80,      // of the clicked track
+      EnsureVisible = 0x100,    // for the clicked track
+      DrawOverlays = 0x200,
+
+      DestroyedCell = 0x8000,     // true if the CLICKED cell was destroyed
+   };
+
+}
+
+
+
+#endif