[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.

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

searx/templates/simple/preferences/engines.html

@@ -57,7 +57,7 @@
               </td>{{- '' -}}
               <th class="name" data-engine-name="{{ search_engine.name }}">
                 {%- if search_engine.enable_http -%}
-                  {{- icon_big('warning', 'No HTTPS') -}}
+                  {{- icon_big('alert', 'No HTTPS') -}}
                 {%- endif -%}
                 <label for="{{ engine_id }}">
                   {{- ' ' -}}{{- search_engine.name -}}