calculate number of monitors; added Mode.h abstract class

modes/Mode.h

@@ -0,0 +1,17 @@
+
+#ifndef MODE_H
+#define MODE_H
+
+#include "GnomeScreensaver.h"
+
+class Mode
+{
+    public:
+        virtual bool expose (GnomeScreensaver & gs) = 0;
+        virtual bool configure (GnomeScreensaver & gs, int width,
+                int height) = 0;
+        virtual bool update (GnomeScreensaver & gs) = 0;
+};
+
+#endif /* MODE_H */
+