[IMP] theme_avantgarde: update the theme

Theme Avantgarde's design has been completely revamped, focusing on
sectors such as the creativity industries, design, architecture, art or
museums, by adding the following improvements:

- Theme layout has changed to 'full'.
- Theme default palette has been changed to 'avantgarde-3'.
- Fonts have been reviewed, using 'Syne' by default and also adding
'Libre Baskerville' and 'Atkinson Hyperlegible' to the theme's font
list.
- Header and footer default values have been reviewed and changed to
'hamburger' (right-aligned) and 'descriptive'.
- Buttons' default design has been revamped, using now outline buttons
by default and removing the previous 'ripple' effect.
- Links are set to default, never using 'underline' decoration.
- Theme's tour has been reviewed and changed, using the following block
configuration: 's_cover' > 's_picture' > 's_three_columns' >
's_text_image' > 's_call_to_action'.
- Theme's snippets used in the tour have been revamped, by using
animated shapes ('s_cover', 's_text_image'), image shapes ('s_picture',
's_text_image'), and a new column design ('s_three_columns').
- Theme's tour snippets have also been optimised to be used in smaller
viewports.
- Theme's screenshot has been updated.

task-2573286

X-original-commit: a707a09059
Part-of: odoo/design-themes#501

theme_avantgarde/__manifest__.py

@@ -16,6 +16,14 @@
         'static/description/poster.jpg',
         'static/description/avantgarde_screenshot.jpg',
     ],
+    'images_preview_theme': {
+        'website.s_cover_default_image': '/theme_avantgarde/static/src/img/pictures/bg_image_08.jpg',
+        'website.s_picture_default_image': '/theme_avantgarde/static/src/img/pictures/bg_image_14.jpg',
+        'website.s_three_columns_default_image_1': '/theme_avantgarde/static/src/img/pictures/bg_image_15',
+        'website.s_three_columns_default_image_2': '/theme_avantgarde/static/src/img/pictures/bg_image_16.jpg',
+        'website.s_three_columns_default_image_2': '/theme_avantgarde/static/src/img/pictures/bg_image_17.jpg',
+        'website.s_text_image_default_image': '/theme_avantgarde/static/src/img/pictures/bg_image_13.jpg',
+    },
     'depends': ['theme_common'],
     'license': 'LGPL-3',
     'live_test_url': 'https://theme-avantgarde.odoo.com',