Don't listen on IPv6 address by default. Prevents network connectivity problems. Closes #1880.

Conflicts:
	src/preferences/advancedsettings.h
	src/preferences/preferences.cpp
	src/preferences/preferences.h
	src/qtlibtorrent/qbtsession.cpp
Split ShutdownConfirmDlg into .h/.cpp files.
Added 'Shutdown now' button in shutdown confirmation dialog. Closes #969.

Conflicts:
	src/qtlibtorrent/qbtsession.cpp
Sync translations from Transifex and run lupdate.