Fix deprecation warnings with wxFont, wxPen, wxBrush ctors...

... Replace some enum constants with the equivalent values from the more
special-purpose enums, as the wx header files recommend, so overloading
selects the ctors with non-int arguments.

In a full rebuild of the debug project on Mac, this reduces the count of
warnings from 264 to 274.

src/export/Export.cpp

@@ -1072,7 +1072,7 @@ void ExportMixerPanel::OnPaint(wxPaintEvent & WXUNUSED(event))
    }
 
    wxColour bkgnd = GetBackgroundColour();
-   wxBrush bkgndBrush( bkgnd, wxSOLID );
+   wxBrush bkgndBrush( bkgnd, wxBRUSHSTYLE_SOLID );
 
    wxMemoryDC memDC;
    memDC.SelectObject( *mBitmap );