Only use one notification

[jancborchardt]

Currently when downloading multiple files, you often end up with 2 notifications: one for the download in progress, and one for the »success« notification of the previous download:

When there is another download coming right after, it is unnecessary to show the success notification. An error notification when something went wrong is enough, and a summary success notification at the end (which of course vanishes like the one currently does.)

cc @davivel @masensio @AndyScherzinger @tobiasKaminsky @stoyicker

[AndyScherzinger]

I think @tobiasKaminsky already took care of this in another PR :)

[tobiasKaminsky]

No, I think you mixed it with the "wait a moment".
In #1168 I have removed the "wait a moment" dialog for removing files as I would otherwise have to keep track of the deleted files to remove the dialog with the last file.

[davivel]

Subsumed by #1468