[fix] simple-theme templates: polish HTML <img> elements

- <img> [1] element does not have an end tag, no need for a leading `/>`
- add global attribute title[2] to result_templates/images.html (result-images-source)
- in jinja macro 'macro result_header' remove duplicate of class="image"
- in jinja macro 'macro result_header' remove alt attribute (fix [3])::

    alt="{{ result.title|striptags }}"

  the result.title is already shown in::

    <h3>{{ result_link(result.url, result.title|safe) }}</h3>

[1] https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img
[2] https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#attr-title
[3] https://github.com/searxng/searxng/issues/523

Closes: https://github.com/searxng/searxng/issues/523
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/templates/simple/infobox.html

@@ -1,6 +1,6 @@
 <aside class="infobox">
   <h2><bdi>{{ infobox.infobox }}</bdi></h2>
-  {% if infobox.img_src %}<img src="{{ image_proxify(infobox.img_src) }}" title="{{ infobox.infobox|striptags }}" alt="{{ infobox.infobox|striptags }}" />{% endif %}
+  {% if infobox.img_src %}<img src="{{ image_proxify(infobox.img_src) }}" title="{{ infobox.infobox|striptags }}" alt="{{ infobox.infobox|striptags }}">{%- endif -%}
   <p><bdi>{{ infobox.content | safe }}</bdi></p>
   {% if infobox.attributes %}
   <div class="attributes">
@@ -8,15 +8,15 @@
     <dl>
       <dt><bdi>{{ attribute.label }} :</bdi></dt>
       {%- if attribute.image -%}
-      <dd><img src="{{ image_proxify(attribute.image.src) }}" alt="{{ attribute.image.alt }}" /></dd>
+      <dd><img src="{{ image_proxify(attribute.image.src) }}" alt="{{ attribute.image.alt }}"></dd>
       {%- else -%}
       <dd><bdi>{{ attribute.value }}</bdi></dd>
       {%- endif -%}
     </dl>
-    {% endfor %}      
+    {% endfor %}
   </div>
   {% endif %}
-  
+
   {% if infobox.urls %}
   <div class="urls">
     <ul>