* Creating a new structure by transforming all the plugins in the
  library using the odoo inheritance system. Plugins are easier to
  implement with the AbstractPlugin to add Odoo behaviors.

* From now on, the methods of the library (in this case Summernote) can
  no longer be called by other modules or files. Only the wysiwyg
  widgets can access it, to simplify the updating process. The wysiwyg
  object serves as an interface.

* Depending on the options the snippets will be loaded or not, the
  editor will be in an iframe or not... all of this is transparent from
  the outside.

* Regarding iframes, all controllers related to editing have been
  removed: the new API no longer needs them. This speeds up loading,
  eases testing and removes complexity for the same
  features.

PUBLIC FEATURES

There are several public methods on the Wysiwyg class:
* Wysiwyg.prepare (WidgetParent): returns a deferred resolved when the
  library (xml, lazy, assets...) is loaded.
* Wysiwyg.getRange (DOM): returns the range (selection in the dom)
* Wysiwyg.setRange (startNode, startOffset, endNode, endOffset): creates
  a range (selection in the dom)
* Wysiwyg.setRangeFromNode (DOM, options) that creates a range from an
  element (option available to select all, start or end)

A jQuery selector was added: :o_editable, which indicates whether the
current element is editable. That is, if it is contained in a tag with
the attribute 'contentEditable = "true"' or in a tag with the class
o_editable.
Several methods are also present:
* focusIn: makes a focus and places the cursor at the beginning of the
  element
* focusInEnd: makes a focus and places the cursor at the end of the
  element
* selectContent: makes a focus and selects the content

HTML FIELD

The HTML field can receive different options:
* style-inline: {boolean} transforms a class into an inline style when
  saving and vice versa when reading.
* no-attachment: {boolean} prevents the use of attachments (in media
  dialog)
* cssEdit: {xml_id} to use a template containing the css to loaded in
  an iframe when editing
* cssReadonly: {xml_id} to use a template containing the css to load
  into an iframe when viewing in readonly
* snippets: {xml_id} snippets template (can be used with or without
  cssEdit)
* wrapper: {template} qweb static template (containing a tag:
  id = "wrapper") that will include the content during editing (removed
  on save)

MASS MAILING

A widget was created for mass mailing. There are now two fields:
body_html and body_arch.
body_arch contains the code with the class without conversion into
inline style, useful when editing and one with the inline style that is
visible in readonly mode and sent by email.
Advantage: no spreading errors, able to update css/theme, able to do
more changes when converting to inline style so that a maximum of mail
clients have an impeccable rendering.

Co-authored-by: Antoine Guenet <age@odoo.com>

After 11.0, in a code editor (ace editor) on the frontend we could not
resize the editor or see line numbers.

This happen since:

- in 64d47c0bc5 ace editor (used when editing code) was updated.
- in ajaxorg/ace@5bf78e09 the line number bar was set aria-hidden
- in 9de1bc0ee aria-hidden element were forcibly hidden

Thus the column of line number (and used for resizeing) in the code
editor was unwillingly hidden.

Since we don't want to make change in library, we fix this in our
custom CSS for the code editor.

opw-1912824
closes #29399

* Simplify the code
* Make the feature mork without unsplash
* Handle corner cases

task-1896705

* web_unsplash, website_sale

- Visual improvements and cleaning in each tab: video, documents,
  pictogram, images.

- Only one search input for both the local library and unsplash.

- Replace the idea of multiple pages by adding a 'Load More' button.

task-1896705

What was designed as a new feature appeared as a regression: users were
not able to choose a bootstrap gray as a background color anymore but
instead got the possibiility to choose a hardcoded gray. This commit
restores the use of the custom gray palette that themes can customize
and which automatically uses the correct text color when used as a
background. This also allows to remove ugly inline style from snippet
definitions and allows to solve bugs like the described below one:

---------------------------------------
Also add bg-* classes on snippet cards:
---------------------------------------

Snippet cards are often put (or may be put by the user) in an element
which have a bg-* class on it. This means that the card will still have
a white background (as chosen by BS4 by default) but the text color will
be adapted to that ancestor bg-* classed element.

This commit forces the card background color (as suggested by BS4) with
bg-* classes.

closes odoo/odoo#27637

Fixing BS behavior in https://github.com/odoo/odoo/commit/e24c3409d915ed73d86077b723b6e0cd77134e80
broke that button color as the button bg was set to transparent, so the
text color was computed to dark instead of light (as it should).