fileutils: migrate to boost::nowide

CMakeLists.txt

README

compat/msvc/package.json

configure.ac

contrib/src/nowide/SHA512SUMS

contrib/src/nowide/package.json

contrib/src/nowide/rules.mak

meson.build

src/archiver.cpp

src/data_transfer.cpp

src/data_transfer.h

src/debug_utils.h

src/fileutils.cpp

src/fileutils.h

src/im/message_engine.cpp

src/jamidht/account_manager.cpp

src/jamidht/archive_account_manager.cpp

src/jamidht/contact_list.cpp

src/jamidht/conversation.cpp

src/jamidht/conversation_module.cpp