jamiaccount: make AccountManager shared, fix onAsync

src/jamidht/account_manager.h

src/jamidht/archive_account_manager.cpp

src/jamidht/archive_account_manager.h

src/jamidht/jamiaccount.cpp

src/jamidht/jamiaccount.h

src/jamidht/server_account_manager.cpp

src/jamidht/server_account_manager.h