Fix compiler warnings

All are harmless but for the sake of clarity have
fixed them all bar a couple;

- Lucene grumbles about signed/unsigned conversion which
  is/isn't valid depending upon the version of CLucene you
  compile with. Either way it is harmless.

- QxtScheduleView has a bunch of issues, but since it is a
  third party widget its better to leave it unchanged.

src/ScatterPlot.cpp

@@ -354,7 +354,6 @@ ScatterPlot::configChanged()
 {
     // setColors bg
     setCanvasBackground(GColor(CPLOTBACKGROUND));
-    QColor grid = GColor(CPLOTGRID);
 }
 
 void