[mod] in the preference page, show !bang of subgrouping categories

The names of the subgrouping categories in the preference page are translated,
to use this categories the user needs to know by which !bang the category can be
selected.  Related to "Make 'non tab category' bangs discoverable" in [#690].

Related:

- [#690] https://github.com/searxng/searxng/issues/690
- https://github.com/searxng/searxng/issues/1604
- https://github.com/searxng/searxng/pull/1545

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/admin/engines/configured_engines.rst

@@ -6,49 +6,66 @@ Configured Engines
 
 .. sidebar:: Further reading ..
 
+   - :ref:`settings categories_as_tabs`
    - :ref:`engines-dev`
    - :ref:`settings engine`
-
-Explanation of the :ref:`general engine configuration` shown in the table
-:ref:`configured engines`.
+   - :ref:`general engine configuration`
 
 .. jinja:: searx
 
-   SearXNG supports {{engines | length}} search engines (of which {{enabled_engine_count}} are enabled by default).
+   SearXNG supports {{engines | length}} search engines of which
+   {{enabled_engine_count}} are enabled by default.
+
+   Engines can be assigned to multiple :ref:`categories <engine categories>`.
+   The UI displays the tabs that are configured in :ref:`categories_as_tabs
+   <settings categories_as_tabs>`.  In addition to these UI categories (also
+   called *tabs*), engines can be queried by their name or the categories they
+   belong to, by using a :ref:`\!bing syntax <search-syntax>`.
+
+.. contents:: Contents
+   :depth: 2
+   :local:
+   :backlinks: entry
+
+.. jinja:: searx
 
    {% for category, engines in categories_as_tabs.items() %}
 
-   {{category}} search engines
+   tab ``!{{category.replace(' ', '_')}}``
    ---------------------------------------
 
-   {% for group, engines in engines | group_engines_in_tab %}
+   {% for group, group_bang, engines in engines | group_engines_in_tab %}
 
    {% if loop.length > 1 %}
-   {{group}}
+   {% if group_bang %}group ``{{group_bang}}``{% else %}{{group}}{% endif %}
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    {% endif %}
 
    .. flat-table::
       :header-rows: 2
       :stub-columns: 1
+      :widths: 10 1 10 1 1 1 1 1 1 1
 
       * - :cspan:`5` Engines configured by default (in :ref:`settings.yml <engine settings>`)
         - :cspan:`3` :ref:`Supported features <engine file>`
 
       * - Name
-        - Shortcut
+        - !bang
         - Module
         - Disabled
         - Timeout
         - Weight
         - Paging
-        - Language, Region
+        - Locale
         - Safe search
         - Time range
 
       {% for mod in engines %}
 
       * - `{{mod.name}} <{{mod.about and mod.about.website}}>`_
+          {%- if mod.about and  mod.about.language %}
+          ({{mod.about.language | upper}})
+          {%- endif %}
         - ``!{{mod.shortcut}}``
         - {%- if 'searx.engines.' + mod.__name__ in documented_modules %}
           :py:mod:`~searx.engines.{{mod.__name__}}`
@@ -56,9 +73,6 @@ Explanation of the :ref:`general engine configuration` shown in the table
           :origin:`{{mod.__name__}} <searx/engines/{{mod.__name__}}.py>`
           {%- endif %}
         - {{(mod.disabled and "y") or ""}}
-          {%- if mod.about and  mod.about.language %}
-          ({{mod.about.language | upper}})
-          {%- endif %}
         - {{mod.timeout}}
         - {{mod.weight or 1 }}
         {% if mod.engine_type == 'online' %}