jamidht: use dht's findCertificate for key lookup

src/client/configurationmanager.cpp

src/jamidht/account_manager.cpp

src/jamidht/account_manager.h

src/jamidht/archive_account_manager.cpp

src/jamidht/connectionmanager.cpp

src/jamidht/jamiaccount.cpp

src/jamidht/jamiaccount.h