Clear segment list & show loading animation in popup on video change

also removed the creatingSegment variable - results in "Start/End Segment Now" correctly updating when using buttons on the controls panel instead
also the "refreshSegments" message no longer sends a response, as we send an update manually now

src/background.ts

@@ -107,6 +107,7 @@ chrome.runtime.onMessage.addListener(function (request, sender, callback) {
         }
         case "time":
         case "infoUpdated":
+        case "videoChanged":
             if (sender.tab) {
                 popupPort[sender.tab.id]?.postMessage(request);
             }