Added a destroy virtual method to all source input plugin main classes

plugins/samplesource/hackrfinput/hackrfinput.cpp

@@ -63,6 +63,11 @@ HackRFInput::~HackRFInput()
 	m_deviceAPI->setBuddySharedPtr(0);
 }
 
+void HackRFInput::destroy()
+{
+    delete this;
+}
+
 bool HackRFInput::openDevice()
 {
     if (m_dev != 0)

plugins/samplesource/hackrfinput/hackrfinput.h

@@ -93,6 +93,7 @@ public:
 
 	HackRFInput(DeviceSourceAPI *deviceAPI);
 	virtual ~HackRFInput();
+	virtual void destroy();
 
 	virtual bool start();
 	virtual void stop();