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.
Don't show availability bar for magnet links

This commit fixes an exception in PropertiesWidget:

"Caught exception in PropertiesWidget::loadDynamicData():  invalid
torrent handle used"

This exception occurs when an user clicks on a torrent that doesn't have
a metadata (when a magnet link is not resolved yet). One should not call
torrent_handle::get_torrent_info when torrent doesn't have a metadata.
Fix crash when the selected torrent disappears from the transfer list. Closes #1661
Fix tracker announcing problem(hit-and-run) when many torrents are being active. Closes #1571
Count magnet links in the 'downloading' filter and make them prevent system inhibition. Closes #1558
Fix compilation with libtorrent 0.15.x.
Rework the GUI code for private torrents.

Conflicts:
	src/qtlibtorrent/qtorrenthandle.cpp
Remove old JSON classes.

Conflicts:
	src/webui/json.cpp
	src/webui/webui.pri
Add QJson files.

Conflicts:
	src/webui/webui.pri
Use new JSON parser/generator. Closes #1395.

Qt4: Use QJson (http://qjson.sourceforge.net).
Qt5: Use native Qt JSON API.

Conflicts:
	src/webui/btjson.cpp
	src/webui/prefjson.cpp
Fix libtorrent 0.15.x compilation.
Update search engines versions.txt file. Closes #1745.
Bring mainwindow in front when notification is clicked and other windows are in front.
Suppress warning about signed/unsigned mismatch.
Manually backport from master, commit 6dabf50 and its fixes. Original author Ivan Sorokin.
Manually backport from master, commit 00e09435 and its fixes. Original author Bruno Barbieri.