Smoother media swap

pico.js

         return
     }
 
-    localStream.getTracks().forEach(track => {
-        track.stop()
-        localStream.removeTrack(track)
-    })
-
+    const oldTracks = localStream.getTracks()
     const addTrack = localStream.addTrack.bind(localStream)
 
     const muted = document.querySelector('#mute-check').checked
             .catch(e => console.error(e))
     }
 
+    oldTracks.forEach(track => {track.stop(); localStream.removeTrack(track)})
     document.querySelectorAll('video').forEach(video => video.srcObject = video.srcObject)
     wire({kind: 'peerInfo', value: {type: 'request'}})
 }