Improve high DPI support in wxAui

Window initial/minimum/maximum sizes are now treated as logical pixels.

Furthermore, many margins and paddings are now converted using
wxWindow::FromDIP() to allow their growth in accord with screen DPI.
This places buttons on toolbars more apart on high DPI screens providing
space for easier touch operations.

Closes https://github.com/wxWidgets/wxWidgets/pull/933

include/wx/aui/dockart.h

@@ -130,6 +130,7 @@ public:
                   wxAuiPaneInfo& pane) wxOVERRIDE;
 
     void DrawIcon(wxDC& dc,
+                  wxWindow *window,
                   const wxRect& rect,
                   wxAuiPaneInfo& pane);