Revert "Fix compilation with libtorrent 0.15.x"

This reverts commit 7ccefae3f896b43843d2cb3b382f3146c84732d1.
Revert "Fix libtorrent 1.0.0 compilation. Closes #1659"

This reverts commit f4a9597ae85efcbce01cd3b1ec0937fc96347328.
﻿Use 'μTP' instead of 'uTP'.
fix issue #1674: AddNewTorrentDialog is shown again and again even if checkbox "dont ask me again" is set
Fix nox build on MAC OSX.