Whole code base: various cleanups, removed SINGLE_SOURCE_COMPILE relicts

* cleaned up code and improved coding style
* removed old SINGLE_SOURCE_COMPILE macro relicts
* use QString::toUtf8() instead of QString::toAscii() wherever possible

src/gui/widgets/visualization_widget.cpp

@@ -1,5 +1,3 @@
-#ifndef SINGLE_SOURCE_COMPILE
-
 /*
  * visualization_widget.cpp - widget for visualization of sound-data
  *
@@ -198,4 +196,3 @@ void visualizationWidget::mousePressEvent( QMouseEvent * _me )
 #include "moc_visualization_widget.cxx"
 
 
-#endif