Fix warnings and modernize demo code

Fix wxFont, wxPen and wxBrush style deprecation warnings.
Add wxFALLTHROUGH to resolve implicit fallthrough warnings in switch statements.
Fix build error when using long for GetTextExtent (with wxUSE_GRID 0).
Remove unused icon from fractal demo.

demos/bombs/bombs.cpp

@@ -218,8 +218,7 @@ BombsCanvas::BombsCanvas(wxFrame *parent, BombsGame *game)
     m_game = game;
     int sx, sy;
     wxClientDC dc(this);
-    wxFont font= BOMBS_FONT;
-    dc.SetFont(font);
+    dc.SetFont(BOMBS_FONT);
 
     wxCoord chw, chh;
     wxString buf = wxT("M");