Fix and enable optimized grid drawing and other minor changes.

* Fix optimized bitmap grid drawing method.
* Enable optimized grid drawing method on Windows and Linux.
* Create a helper class for resetting and restoring device context scale
  and origin settings for blitting purposes.
* Use wxLogTrace instead of wxLogDebug for coordinate dumping in
  drawpanel.cpp.  See comments for more information on enabling coordinate
  tracing.
* Add flag to allow hiding the drawing cross hair.  Hide cross hair by
  default on OSX.
* Move get cross hair device position code from draw panel object to base
  screen object.
* Remove redundant parent member variable from draw panel object by
  overriding wxWindow::GetParent() method.

eeschema/find.cpp

@@ -198,7 +198,7 @@ SCH_ITEM* SCH_EDIT_FRAME::FindComponentAndItem( const wxString& component_refere
         wxPoint old_cursor_position    = sheet->LastScreen()->m_Curseur;
         sheet->LastScreen()->m_Curseur = pos;
 
-        curpos = DrawPanel->CursorScreenPosition();
+        curpos = GetScreen()->GetCrossHairScreenPosition();
 
         DrawPanel->GetViewStart( &( GetScreen()->m_StartVisu.x ),
                                  &( GetScreen()->m_StartVisu.y ) );