It is more consistent to have this code closer to the xmpp protocol handling.

 - when a new contact with higher prio connect, detach session from chat control. Fixes #5021
 - don't re-use a session that was for another sessin

Tests are more than welcome!

prevent a traceback when we get a wrong disco#info reply (a feature without a var attribute). Fixes #5232

[Mattj & Florob] fix canonicalize function to prevent having twice xmlns in the attributes. Fixes #4396

stop sending chatstates when remote server doesn't respond anymore. Don't acknoledge error message receipes. Fixes #4064

request bookmarks via XML if server announce it supports pubsub but doesn't answer in the next 30 seconds. Fixes #5198

If the number of connected resources is appended in parentheses,
the appropriate ltr or rtl mark is inserted before, so that the
writing direction at the end of the nickname matches the writing
direction of the whole displayed string as determined by
http://www.unicode.org/reports/tr9/#The_Paragraph_Level