[REF] devtools: Better messages forwarding

This commit improves how messages are relayed from the page to the
devtools by using a specific port for each instance of the owl devtools
panel and refreshing it through the heartbeat message. This allows
to prevent sending messages to every devtools instances and sorting
the messages inside.

tools/devtools/src/devtools_app/devtools.js

@@ -27,7 +27,6 @@ function createPanelsIfOwl() {
         "../../assets/icon128.png",
         IS_FIREFOX ? "devtools_panel.html" : "devtools_app/devtools_panel.html"
       );
-      browserInstance.runtime.sendMessage({ type: "newDevtoolsPanel" });
     }
   );
 }