The gallery slider index was wrongly calculated when the gallery had no
active element, as the jquery method .index() will still return -1 when
no element is found.

task-2472041

closes odoo/odoo#67389

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

- Go to the website
- Drag a "Tabs" block on the page, you will have 3 example tabs
- Click on the tab "Contact" and drag in the block "Image Gallery"
- Add multiple images to the image gallery
- Click on one of the other tabs so that the image gallery is hidden
- Save

The image gallery do not have the thumbails anymore.
This occurs because when the carousel-indicator is hidden, jquery is not
able to fetch its real length, so no icons are added.

opw-2438513

closes odoo/odoo#66197

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

* Prior to this commit, Snippets XML Qweb templates files were located
  under website/static/src/xml/.

* After this commit, Snippets XML Qweb templates files will be named
  AAA.xml (with AAA being the revision number) and located under the
  related Snippet directory '/website/static/src/snippets/SNIPPET_DIRECTORY/'

task-2276740
PR #53175

Add dots indicators in gallery snippet options.

Part of https://github.com/odoo/odoo/pull/45096
task-2162952

Review the gallery snippet. It has been improved in multiple ways.
Added new options, etc.

Part of https://github.com/odoo/odoo/pull/45096
task-2162952

In gallery snippet with slideshow mode, the right/left indicators have
now the same behavior in editor and outside. Before this commit, these
indicators were always visible in editable mode.

Part of https://github.com/odoo/odoo/pull/45096
task-2162952

Before this commit there was a traceback when rendering the lightbox
in the gallery snippet. This bug was introduced by the new media dialog
system.

Related to task-2162952

closes odoo/odoo#51603

X-original-commit: 791ecf72af4a0928a02bf1bbdc269c67fcc3524c
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>