[IMP] reference/user_interface: reformat and clarify views reference

In particular, the following changes are made:
- Use definition lists to define view types;
- Use the `class` and `attribute` admonitions to define classes,
  views' root attributes, views' components, and attribute values;
- Extract repetitive content to included RST files;
- Restructure and rewrite the explanations, and insert necessary
  admonitions, when they lack clarity;
- Display SVG images into dedicated admonitions;
- Fix RST and English mistakes;
- Rename `view_architecture` to `view_architectures`, as it lists all
  existing architectures;
- Replace underscores with hyphens in image file names.

task-3458320

Author: AntoineVDV

content/developer/reference/backend/data.rst

@@ -236,7 +236,7 @@ Defines an ``ir.ui.menu`` record with a number of defaults and fallbacks:
 ``template``
 ------------
 
-Creates a :ref:`QWeb view <reference/view_architecture/qweb>` requiring only the ``arch``
+Creates a :ref:`QWeb view <reference/view_architectures/qweb>` requiring only the ``arch``
 section of the view, and allowing a few *optional* attributes:
 
 ``id``

content/developer/reference/external_api.rst

@@ -1112,7 +1112,7 @@ Provides information about Odoo models via its various fields.
     list of the model's fields through a :class:`~odoo.fields.One2many` to
     :ref:`reference/webservice/inspection/fields`
 ``view_ids``
-    :class:`~odoo.fields.One2many` to the :doc:`../reference/user_interface//view_architecture`
+    :class:`~odoo.fields.One2many` to the :doc:`../reference/user_interface/view_architectures`
     defined for the model
 ``access_ids``
     :class:`~odoo.fields.One2many` relation to the

content/developer/reference/frontend/qweb.rst

@@ -675,7 +675,7 @@ Request-based
 
 Most Python-side uses of QWeb are in controllers (and during HTTP requests),
 in which case templates stored in the database (as
-:ref:`views <reference/view_architecture/qweb>`) can be trivially rendered by calling
+:ref:`views <reference/view_architectures/qweb>`) can be trivially rendered by calling
 :meth:`odoo.http.HttpRequest.render`:
 
 .. code-block:: python

content/developer/reference/user_interface.rst

@@ -8,6 +8,6 @@ User interface
     :titlesonly:
 
     user_interface/view_records
-    user_interface/view_architecture
+    user_interface/view_architectures
     user_interface/scss_inheritance
     user_interface/icons

content/developer/reference/user_interface/icons.rst

@@ -1,5 +1,7 @@
 :hide-page-toc:
 
+.. _reference/user_interface/ui_icons:
+
 ========
 UI icons
 ========