Don't fail badly when we didn't manage to connect to the chat

[sampaccoud]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.
When connection to the chat fails (happens on private tabs with drastic limitations on cross site iframes), we should not fail badly

Describe the solution you'd like
We should detect this situation and display a button "start chatting". A click on the link should open a new tab and connect directly to marsha without the iframe.