Implemented OpenCV demo to demonstrate video device listing and set up code structure for video

src/execute.c

@@ -77,6 +77,10 @@ static struct cmd_func chat_commands[] = {
     { "/hangup",    cmd_hangup      },
     { "/mute",      cmd_mute        },
     { "/sense",     cmd_sense       },
+#ifdef VIDEO
+    { "/enablevid", cmd_enablevid   },
+    { "/disablevid",cmd_disablevid  },
+#endif /* VIDEO */
 #endif /* AUDIO */
     { NULL,         NULL            },
 };