Also add flush method to converse.js (used in ClientStorage tests)

Can succesfully connect now, but still need to get rid of ajax calls to @@xmp-userinfo, and replace them with
VCards.

This is necessary because each open tab in the browser is its own resource.

TODO: Ideally we should differentiate between resources in the browser (using
converse.js) and other resources (i.e from a desktop client).

- This allows multiple open tabs (which is each its own resource) to be aware
when one tab sent a message.