swarm: synchronize conversations between devices

src/jamidht/account_manager.cpp

src/jamidht/account_manager.h

src/jamidht/archive_account_manager.cpp

src/jamidht/archive_account_manager.h

src/jamidht/connectionmanager.cpp

src/jamidht/conversation.cpp

src/jamidht/jamiaccount.cpp

src/jamidht/jamiaccount.h

test/unitTest/Makefile.am

test/unitTest/syncHistory/syncHistory.cpp