Remove extraneous '/' added by Pidgin to XMPP accounts
Bugfix: Speakers were not moved in the RawConversation move constructor
Added support for messages in RawConversation

For now, only an "opaque" (unstructured) system message type is supported.
Pidgin Text Format decoder: Added parsing of messages

System messages are not inspected for structure yet. Will add this in a
future commit.