[#3649] Implement unserialize method for accounts

sflphone-common/src/account.h

sflphone-common/src/config/config.cpp

sflphone-common/src/config/serializable.h

sflphone-common/src/config/yamlnode.h

sflphone-common/src/config/yamlparser.cpp

sflphone-common/src/config/yamlparser.h

sflphone-common/src/iax/iaxaccount.cpp

sflphone-common/src/iax/iaxaccount.h

sflphone-common/src/managerimpl.cpp

sflphone-common/src/managerimpl.h

sflphone-common/src/managerimpl_registration.cpp

sflphone-common/src/sip/sipaccount.cpp

sflphone-common/src/sip/sipaccount.h

sflphone-common/test/configurationtest.cpp