Remove QsLog destinations when they are destroyed.

This fixes some issues where MultiMC was segfaulting on exit because
things were trying to write to the logger while they were being destroyed,
but the destinations had already been destroyed and were left in the list.

logger/QsLogDest.cpp

@@ -25,6 +25,7 @@
 
 #include "QsLogDest.h"
 #include "QsDebugOutput.h"
+#include "QsLog.h"
 #include <QFile>
 #include <QTextStream>
 #include <QString>
@@ -32,6 +33,12 @@
 namespace QsLogging
 {
 
+Destination::~Destination()
+{
+	Logger::instance().removeDestination(this);
+	QsDebugOutput::output("Removed logger destination.");
+}
+
 //! file message sink
 class FileDestination : public Destination
 {