erp5_web_jabber_client: work for for avoiding messages loss

Add Semaphore functionality on adding Log to history.

Implementation of Delivery Receipt sending. Delivery Receipt hadnling is not implemented yet. http://xmpp.org/extensions/xep-0184.html

clients which support xep-0184 adnroid: https://conversations.im/ https://www.xabber.com/ linux: http://psi-plus.com/