Implement receiver HID++ connect/disconnect events

Many changes were made here but that was the biggest one.

There's currently a bug where std::system_error: Broken pipe is thrown
after launching the daemon with a receiver connector.

A workaround for this bug is to simply shake the mouse while starting
the daemon. I will investigate this soon.

src/logid/Receiver.h

@@ -2,14 +2,21 @@
 #define LOGID_RECEIVER_H
 
 #include <string>
+#include "backend/dj/ReceiverMonitor.h"
+#include "Device.h"
 
 namespace logid
 {
-    class Receiver
+    class Receiver : public backend::dj::ReceiverMonitor
     {
     public:
         Receiver(std::string path);
+
+    protected:
+        virtual void addDevice(backend::hidpp::DeviceConnectionEvent event);
+        virtual void removeDevice(backend::hidpp::DeviceIndex index);
     private:
+        std::map<backend::hidpp::DeviceIndex, std::shared_ptr<Device>> _devices;
         std::string _path;
     };
 }