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.
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.