Web API: use message passing to start/stop device for all the rest of device plugins

plugins/samplesource/filesource/filesourceinput.h

@@ -155,6 +155,25 @@ public:
 		{ }
 	};
 
+    class MsgStartStop : public Message {
+        MESSAGE_CLASS_DECLARATION
+
+    public:
+        bool getStartStop() const { return m_startStop; }
+
+        static MsgStartStop* create(bool startStop) {
+            return new MsgStartStop(startStop);
+        }
+
+    protected:
+        bool m_startStop;
+
+        MsgStartStop(bool startStop) :
+            Message(),
+            m_startStop(startStop)
+        { }
+    };
+
 	class MsgReportFileSourceStreamData : public Message {
 		MESSAGE_CLASS_DECLARATION