Update conversejs

[tyler274]

If its not terribly difficult its been about a year since the last converse update was merged,

Thanks

[seocam]

It shouldn't be that hard I'm just not with enough time for that :(

Help is welcome here!

[vhf]

I could give a shot at a PR if you tell me what to do.

[seocam]

Basically you would have to update the files in conversejs/static/converse.js with the most recent converse.js release (https://github.com/jcbrand/converse.js/releases). Them we have to test it manually because unfortunately we don't have automated tests so far.

And finally update the readme and changes files.