[IMP] survey: improve sessions usability and design

PURPOSE

Improve the various sessions flow to make it easier for attendees to reach the
session and to allow better interactions between the host and his audience.

This comes with small usability improvements as well as increased
"beautifulness" by using custom layouts & animations.

SPECS

General specifications, see sub-commits for details.

- Currently, the "short link" feature is good but it still needs to be improved
  with the following points:
    - Make the default "code" shorter (4) and digit only.
    - Allow to customize the "code"
    - Check for potential collisions
- When attendees reach the survey through the code, they need to land on the
  "waiting screen" even if the session is not started yet. This will allow the
  host to show the survey link even if he forgets to click on "start session"
  first.
- Reduce the fade out / fade in delay when moving from one question to another.
  It's currently 2 seconds, change it to 1 second.
  Right now the delay gives a "slowness" impression.
- Display matrix choices on the host screen.
  It will allow attendees that are not participating to have more context.
- Add python test/tours to test the survey session flow from the host point of view
- Improve survey form navigation (moved buttons, added keyboard navigation)
- Auto submit questions and matrix with simple choice

DESIGN TWEAKS

Slightly improve the survey form by adding a few cosmetic changes,
notably:

- Add/reduce some margins/paddings
- Adjust colors/font-weight
- Adjust heights
- Change some icons by more fitting replacements
- Center matrix choices
- Move survey progression to bottom-right
- Remove ugly jumbotrons
- Hide survey title in page_per_question layout
- When there are 5 or less option for simple_choice or multiple_choice
  questions, display the options vertically.
- Only show the textarea for the "comment answer" if the user clicks on the
  related option.

LINKS

Upgrade PR odoo/upgrade#897
Task 2208574

closes odoo/odoo#46768

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>