Splitting mSelIndex

Using mTextEditIndex for tracking active text box index, and mNavigationIndex used to track selection for keyboard navigation purposes
See #1195

src/menus/EditMenus.cpp

@@ -46,7 +46,7 @@ bool DoPasteText(AudacityProject &project)
    for (auto pLabelTrack : tracks.Any<LabelTrack>())
    {
       // Does this track have an active label?
-      if (LabelTrackView::Get( *pLabelTrack ).HasSelection( project )) {
+      if (LabelTrackView::Get( *pLabelTrack ).GetTextEditIndex(project) != -1) {
 
          // Yes, so try pasting into it
          auto &view = LabelTrackView::Get( *pLabelTrack );

src/menus/LabelMenus.cpp

@@ -346,7 +346,7 @@ void OnPasteNewLabel(const CommandContext &context)
       // Unselect the last label, so we'll have just one active label when
       // we're done
       if (plt)
-         LabelTrackView::Get( *plt ).SetSelectedIndex( -1 );
+         LabelTrackView::Get( *plt ).ResetTextSelection();
 
       // Add a NEW label, paste into it
       // Paul L:  copy whatever defines the selected region, not just times