[web-client] simple theme: refactor jinja_svg_catalog and cleanup icon names

This patch implements the template generation of the template:

  searx/templates/simple/icons.html

by the way the icon set (the icon names) has been normalized:

  film-outline   --> film
  magnet-outline --> magnet
  ..
  warning        --> alert

Some missing (categorie) icons had been added.

Some of the ionicons are not suitable for a dark theme, we fixed the svg
manually in src/svg/ionicons:

- https://github.com/searxng/searxng/pull/4284#issuecomment-2680550342

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

searx/templates/simple/preferences.html

@@ -21,7 +21,7 @@
 
 {%- macro checkbox(name, checked, disabled) -%}
   {%- if checked == '?' -%}
-    {{- icon_small('warning') -}}
+    {{- icon_small('alert') -}}
   {%- else -%}
     <input type="checkbox" {%- if name %} name="{{ name }}" {%- endif %} value="None" {%- if checked %} checked {%- endif -%}{%- if disabled %} disabled {%- endif -%}>
   {%- endif -%}
@@ -128,7 +128,7 @@
     <td class="{{ label }} column-reliability">{{- '' -}}
       <a href="{{ url_for('stats', engine=engine_name|e) }}">{{- '' -}}
         <span>
-          {{- icon_big('warning', 'The engine is not reliabled') }} {{ r -}}
+          {{- icon_big('alert', 'The engine is not reliabled') }} {{ r -}}
         </span>{{- '' -}}
       </a>{{- '' -}}
       <div class="engine-tooltip" role="tooltip" id="{{engine_name}}_reliability">