Add serialization on matrix events

include/Deserializable.h

include/events/AliasesEventContent.h

include/events/AvatarEventContent.h

include/events/CanonicalAliasEventContent.h

include/events/CreateEventContent.h

include/events/Event.h

include/events/HistoryVisibilityEventContent.h

include/events/JoinRulesEventContent.h

include/events/MemberEventContent.h

include/events/MessageEventContent.h

include/events/NameEventContent.h

include/events/PowerLevelsEventContent.h

include/events/RoomEvent.h

include/events/StateEvent.h

include/events/TopicEventContent.h

src/events/AliasesEventContent.cc

src/events/AvatarEventContent.cc

src/events/CanonicalAliasEventContent.cc

src/events/CreateEventContent.cc

src/events/HistoryVisibilityEventContent.cc