[simple theme] update to ion icons 5 and drop webfont

* update from ionicons-npm to ionicons ver.5
* drop the webfont built by grunt for icons
* built icons.html template for inlining icons with jinja2 into html
* update icon to use mostly the outline version
* add icons to categories and do not display them on mobile to save space
* remove all legacy ion icon font files from simple theme
* icons.html is added in this commit since make statc.build.restore requires git to know the file already
* cleanup error-dialog

searx/templates/simple/messages/no_results.html

@@ -1,17 +1,19 @@
-{% from 'simple/macros.html' import icon %}
+{% from 'simple/icons.html' import icon_big %}
 {% if unresponsive_engines %}
 <div class="dialog-error" role="alert">
-  <p><strong>{{ _('Error!') }}</strong> {{ _('Engines cannot retrieve results.') }}</p>
-  {% for engine_name, error_type in unresponsive_engines %}
-  <p>{{- '' -}}
-    {{- engine_name }} (
+  {{ icon_big('warning') }}
+  <div>
+    <p><strong>{{ _('Error!') }}</strong> {{ _('Engines cannot retrieve results.') }}</p>
+    {% for engine_name, error_type in unresponsive_engines %}
+    <p>{{- '' -}}
+      {{- engine_name }} (
       <a href="{{ url_for('stats', engine=engine_name|e) }}" title="{{ _('View error logs and submit a bug report') }}">
-          {{- error_type -}}
+        {{- error_type -}}
       </a> ){{- '' -}}
-  </p>
-  {%- endfor %}
-
-  <p><small>{{ _('Please, try again later or find another SearXNG instance.') }} (<a href="{{ get_setting('brand.public_instances') }}">{{ _('Public instances') }}</a>) </small></p>
+    </p>
+    {%- endfor %}
+    <p><small>{{ _('Please, try again later or find another SearXNG instance.') }} (<a href="{{ get_setting('brand.public_instances') }}">{{ _('Public instances') }}</a>) </small></p>
+  </div>
 </div>
 {% else %}
 <div class="dialog-error" role="alert">