simplify Clear() in Window and its derivatives

it removes argument responsible for immediate refreshing.
since after all calls that were refreshing screen there was
call to Refresh() anyway, this switch doesn't make much sense.

src/scrollpad.h

@@ -102,10 +102,9 @@ namespace NCurses
 			virtual void Resize(size_t new_width, size_t new_height);
 			
 			/// Cleares the content of scrollpad
-			/// @param clear_screen indicates whether window has to be cleared imediately or not
 			/// @see Window::Clear()
 			///
-			virtual void Clear(bool clear_screen = 1);
+			virtual void Clear();
 			
 			/// Sets starting position to the beginning
 			///