Fix Windows file associations creation.

Now qBittorrent create global ProgId during installation (using HKLM hive)
and allow to associate .torrent files with it (using HKCU).
Fix alertdispatcher.cpp compilability on Qt5.
Fix column resizing issues
Scan Folder dialog now remembers last location

Also fix fs_utils spacing
Merge pull request #1824 from bryanroscoe/rememberLocation

Scan Folder dialog now remembers last location
Fix possible crashes. Closes #1814.
Remove deprecated feature of separate DHT port.
Sync translations from Transifex.
Run lupdate.
Merge pull request #1782 from sorokin/alert-disp-qt5

Fix alertdispatcher.cpp compilability on Qt5.
Merge pull request #1470 from glassez/assoc

Fix Windows file associations creation
Installer correctly associates torrents and magnet links with qBittorrent under non-admin accounts. Closes #291 #527 #579 #614 #964.
Cache preferences in memory. Closes #1272, #1523, #1694.
Migrate everything to use the new Preferences class and not access directly the qbittorrent.ini file.
Migrate everything to use the new Preferences class and not access directly the qbittorrent.ini file.(webui)
Fix compilation on MACOS.
Fix checkbox for 'Copy .torrent files to' setting, which was broken by b70621. Closes #1748.
Limit max cache to 1800MiB for 32bits compiled binaries and to 4GiB for other. Closes #1698.
Allow disabling of OS cache. This will prevent RAM increases on Windows when seeding many files. Closes #1699.
Sync translations from Transifex.