misc: use string_view

src/account.h

src/account_factory.cpp

src/account_factory.h

src/jamidht/conversation.cpp

src/jamidht/conversation.h

src/jamidht/jamiaccount.cpp

src/jamidht/jamiaccount.h

src/jamidht/jamiaccount_config.h

src/manager.cpp

src/sip/sipaccount.cpp

src/sip/sipaccount.h

src/sip/sipaccount_config.h

src/sip/sipvoiplink.cpp