Fix heap-buffer-overrun in PropertiesWidget::displayFilesListMenu
Change the program updater's URL for Windows and Mac OS X. Closes #1954.
Fewer calls to torrent_handle::info_hash()
Use std::vector instead of std::deque in QAlertDispatcher

As we never use {push,pop}_front std::vector works here perfectly.
Also reserve memory for std::vector out of lock.

This could be considered as an optimization, but in reality this is just
using right container in right place. According to my measurements total
speedup is under 0.2%.
Fix race condition in QAlertDispatcher

It was possible that QAlertDispatcher::dispatch() could access (lock)
mutex that was destroyed by main thread. Fix this by moving mutex into a
tag.
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
adding a save resume data interval option

because some SSD users oppose frequent disk writes
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.
Remove unneccessary includes of libtorrent in misc.h
Remove inclusion of <QThread> from misc.h
Make alertdispatcher.h self contained and replace include libtorrent/session with forward declaration