Re: late coming features

Here is a quick look at the documentation impact of the notification changes:

- getting started: the 'respond to messages' video and page will have
to be dropped or redone

- introduction:
  - the clock, calendar and appointments section should include
notifiications (needs a new screenshot)}
  - the message tray section should be dropped

- the notifications and message tray section needs to be redone

- the useful keyboard shortcuts section should be updated for Super-M
to not mention the message tray

- activities, dash, top bar... section should be updated to not
mention the message tray

- calendar appointments needs a new screenshot