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

Though I consider this a major regression, as using doc-strings is a much
cleaner and better solution. It requires not that big scaffolding to support it,
but some of Gajim developers think otherwise.

[praveen & I] ability to Ctrl+ H / I in roster to show history or information dialog of a contact. Fixes #5301

The reworked version has refactored and simplified architecture, which also
involves simplified dispatching.

add a graphics optio nto all print text function to not display emoticons and latex formulas in nicks. Fixes #4651

[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