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.

common/drawframe.cpp

@@ -727,12 +727,12 @@ void EDA_DRAW_FRAME::LoadSettings()
     bool btmp;
 
     if ( cfg->Read( m_FrameName + ShowGridEntryKeyword, &btmp ) )
-        SetGridVisibility( btmp);
+        SetGridVisibility( btmp );
 
     int itmp;
 
     if( cfg->Read( m_FrameName + GridColorEntryKeyword, &itmp ) )
-        SetGridColor(itmp);
+        SetGridColor( itmp );
 
     cfg->Read( m_FrameName + LastGridSizeId, &m_LastGridSizeId, 0L );
 }