New Reload source function

Generalize the reload of stream source to all types of sources. Enable OSC command to reload source.

src/SessionSource.h

@@ -44,6 +44,7 @@ public:
 
     // SessionFile Source specific interface
     void load(const std::string &p = "", uint level = 0);
+    void reload () override;
 
     inline std::string path() const { return path_; }