Hangs when click start collab

When we start a collaboration, it would be usefull to change the text of the button (or to let user know somehow), that something is going on.

Right now it just seems like nothing is happening until the chat eventually pops up.

Run the mi2b2 viewer and reproduce the delay after clicking the start-collaboration button. Trace that button into the chat-opening flow; done means users receive visible progress feedback while collaboration starts, and the chat still appears afterward.

Written by the indexing model from the issue text.