Limit max cache to 1800MiB for 32bits compiled binaries and to 4GiB for other. Closes #1698.

Conflicts:
	src/preferences/advancedsettings.h
	src/preferences/preferences.cpp
Allow disabling of OS cache. This will prevent RAM increases on Windows when seeding many files. Closes #1699.

Conflicts:
	src/preferences/advancedsettings.h
	src/preferences/preferences.cpp
	src/preferences/preferences.h
	src/qtlibtorrent/qbtsession.cpp
Sync translations from Transifex.
Run lupdate.