rename autoComplete directive as tabComplete to avoid confusion with the autocomplete html attribute

Make event stream storage return all membership events about the user, regardless of if they were in the room or not.

Define __copy__ and __deepcopy__ as identity functions on DomainSpecificString, so that copy.deepcopy() will work on them

Create a placeholder for each image of the chat thread. The height of this placeholder is the height of the image so that the scroller position will not be disrupted when the image will be actually loaded and displayed in its full height