Moved the Qwt widget in ACG to its own directory

Only include this directory if qwt is available

git-svn-id: http://www.openflipper.org/svnrepo/OpenFlipper/branches/Free@19088 383ad7c9-94d9-4d36-a494-682f7c89f535

QwtFunctionPlot.hh

@@ -81,7 +81,7 @@
 // #include "QtFunctionPlotBase.hh"
 
 #if QWT_VERSION >= 0x060000
- #include <ACG/QtWidgets/QwtHistogramm.hh>
+ #include <ACG/QwtWidgets/QwtHistogramm.hh>
 #else
  #include "HistogramItem.hh"
 #endif