Use system copy of qtsingleapplication.

--- a/sialantools/sialantools.pri
+++ b/sialantools/sialantools.pri
@@ -1,4 +1,5 @@
 QT += qml quick
+CONFIG += qtsingleapplication
 
 android {
     manifest.source = android-build
@@ -24,20 +25,10 @@
 
             HEADERS += \
                 sialantools/sialanmimeapps.h \
-                sialantools/qtsingleapplication/qtsinglecoreapplication.h \
-                sialantools/qtsingleapplication/qtsingleapplication.h \
-                sialantools/qtsingleapplication/qtlockedfile.h \
-                sialantools/qtsingleapplication/qtlocalpeer.h
 
             SOURCES += \
                 sialantools/sialanmimeapps.cpp \
-                sialantools/qtsingleapplication/qtsinglecoreapplication.cpp \
-                sialantools/qtsingleapplication/qtsingleapplication.cpp \
-                sialantools/qtsingleapplication/qtlockedfile.cpp \
-                sialantools/qtsingleapplication/qtlocalpeer.cpp
 
-            win32: SOURCES += sialantools/qtsingleapplication/qtlockedfile_win.cpp
-            unix:  SOURCES += sialantools/qtsingleapplication/qtlockedfile_unix.cpp
         }
     }
 }

--- a/sialantools/sialanapplication.h
+++ b/sialantools/sialanapplication.h
@@ -22,7 +22,7 @@
 #include "sialan_macros.h"
 
 #ifdef DESKTOP_DEVICE
-#include "qtsingleapplication/qtsingleapplication.h"
+#include "qtsingleapplication.h"
 class INHERIT_QAPP : public QtSingleApplication
 {
 public: