dring: add conversation interface API

src/account.h

src/client/CMakeLists.txt

src/client/Makefile.am

src/client/conversation_interface.cpp

src/client/ring_signal.cpp

src/client/ring_signal.h

src/dring/conversation_interface.h

src/gittransport.cpp

src/jamidht/CMakeLists.txt

src/jamidht/Makefile.am

src/jamidht/conversation.cpp

src/jamidht/conversation.h

src/jamidht/conversationrepository.cpp

src/jamidht/conversationrepository.h

src/jamidht/jamiaccount.cpp

src/jamidht/jamiaccount.h

src/manager.cpp

src/sip/sipaccountbase.cpp

src/sip/sipaccountbase.h

test/unitTest/Makefile.am