Improvements to the receive mode web frontend

[SaptakS]

When sending relatively big files, the receive mode web frontend (i.e. the frontend that the sender of the file sees) has some issues which I feel can be improved.

In the above screenshot, we can see that the sending of the file to the person running receive mode hasn't completed since it's traversing through the Tor network. However, the progress bar is complete. We should probably better indicate that the sending is still in progress and also mention not to close the Tor Browser till it's fully sent.