When cloning a snippet section thanks to the editor, the associated
snippet options' `on_clone` methods are called. Now these methods
receive a new argument `options`. The option this commit introduces
is the `isCurrent` one. It allows the method to know if the snippet
section it is associated to is the one that was cloned or if it is a
child of the one that was cloned.

This is useful to solve a known bug when cloning elements which have
bootstrap columns:

- When one column is cloned we want it to lose its col-*-offset-*
  classes so that the offset is not duplicated (only the column).

- When a container with column children is cloned we do not want
  these column' offsets to be removed (we want the whole cloned
  container to be the same).

Fixed some issues with parralax image updates:

- Background updated without clicking
- Default wallpaper not coming back
- Background disappearring sometimes

In carousel snippet, the target element for background snippet option is
being changed manually. So for the new target, we have to rebind the
associated events that were bound in `start` function of the snippet
option. For that, some code is extracted from the `start` function and
is used to rebind necessary events for new targets.

In particular, this was preventing the carousel slides' backgrounds to
be automatically removed when a background-color was selected.

A forward-port ported this commit:
https://github.com/odoo/odoo/commit/c12f2cd5ccc72a680ab741b4ce16d3913dd3854e#diff-473476fda8a8b38a9ee4480eb2bf2e2eR150
But ignored that a more recent one did remove the related code:
https://github.com/odoo/odoo/commit/0eafeab1#diff-473476fda8a8b38a9ee4480eb2bf2e2eL173

The result was misindented breaking code.