build: search headers in all source directories

* removed paths in include directives
* changed cmake to provide necessary header search paths
* changed name of version.h to productVersion.h due to name conflict

src/lib_gui/qt/element/QtCodeArea.h

@@ -4,8 +4,8 @@
 #include <memory>
 #include <vector>
 
-#include "qt/element/QtCodeField.h"
-#include "qt/utility/QtScrollSpeedChangeListener.h"
+#include "QtCodeField.h"
+#include "QtScrollSpeedChangeListener.h"
 
 class QDragMoveEvent;
 class QPaintEvent;