plugin chat: first draft: - only one 2 one display is handled for now - own messages are displayed in blue, other ones in gray - by default we display our own jid (for now) - to change target, contact in contact widget can be clicked, or a jid can be entered in header input - disco is called on jid entered in header, if it's a conference a MUCJoin will be called (not implemented yet), else a new chat widget with the jid replace the current one