Fix TorrentReactor search plugin
Replace deprecated sgmllib with HTMLParser/html.parser
Fix search engine encoding issues with python3 on Windows

Closes #1996
Pirate bay search engine update
Remove unneeded tooltip
Fix search inconsistency between Python versions

Closes #2012
Don't stretch the last section in the transfer list

Since the content of some sections is right aligned, automatically
resizing the width of the last one to fill the header could be
sometimes undesired.

Let the user choose the width of each section and never change his
preference.
Set minimum width of the left panel in the preferences

Change also the default width and set it to the minimum.
This minimum width prevents the horizontal scrollbar from appearing.

The size of the items in the list depends on the Qt style, so the
left panel could be few pixels larger than required with some of them.
Allow relative torrent paths when qBittorrent is already running

Adding new torrents from the command line while qBittorrent was
already running was possible only providing the absolute path to
the file.
Make Windows icons suitable for high dpi screens

The maximum size of the icons is now 256x256 pixels so that
Windows can correctly scale them.

The 256x256 layer for the main icon was created upscaling the
192x192 png available in the source tree. Hence, the icon might
not be perfect at the maximum size.

The icon for the file association was made from scratch and it's
visually similar to the previous icon.
Increase maximum size of system icons

System icons were limited to a size 24x24 pixels, while the embedded
icons are 32x32 pixels big.
Use the correct character encoding for exceptions coming from libtorrent.

Conflicts:
	src/qtlibtorrent/qbtsession.cpp
Optimize misc::naturalSort()

Previous implementation used QRegExp to find a first digit. That is
utterly ineffective.

When torrent list is sorted by name (a column that uses the naturalSort() for
comparison), naturalSort could take 18.6% of the time of the UI thread. Optimize it
so now it takes 1% of the time of the UI thread.
Don't show multiple unlock UI dialogs. Closes #2040.
Use boost:bind() as the docs show. Allows compilation with older gcc versions.

Conflicts:
	src/torrentcreator/torrentcreatorthread.cpp