Bug + HTML corrections

Add alt on favicon.
Use correct datetime format
Remove pubdate tag
Use url instead of pretty_url for web.archive.org
Add alt on video image

searx/templates/oscar/result_templates/videos.html

 {% from 'oscar/macros.html' import icon %}
 
-<h4 class="result_header">{% if result['favicon'] %}<img width="32" height="32" class="favicon" src="static/{{ theme }}/img/icons/{{ result['favicon'] }}.png" /> {% endif %}<a href="{{ result.url }}">{{ result.title|safe }}</a></h4>
+<h4 class="result_header">{% if result['favicon'] %}<img width="32" height="32" class="favicon" src="static/{{ theme }}/img/icons/{{ result['favicon'] }}.png" alt="{{ result['favicon'] }}" /> {% endif %}<a href="{{ result.url }}">{{ result.title|safe }}</a></h4>
     
-{% if result.publishedDate %}<time class="text-muted" datetime="{{ result.publishedDate }}" pubdate>{{ result.publishedDate }}</time>{% endif %}
-<small><a class="text-info" href="https://web.archive.org/web/{{ result.pretty_url }}">{{ icon('link') }} {{ _('cached') }}</a></small>
+{% if result.publishedDate %}<time class="text-muted" datetime="{{ result.pubdate }}" >{{ result.publishedDate }}</time>{% endif %}
+<small><a class="text-info" href="https://web.archive.org/web/{{ result.url }}">{{ icon('link') }} {{ _('cached') }}</a></small>
 
 <div class="container-fluid">
     <div class="row">
-        <img class="thumbnail col-xs-6 col-sm-4 col-md-4 result-content" src="{{ result.thumbnail|safe }}" />
+        <img class="thumbnail col-xs-6 col-sm-4 col-md-4 result-content" src="{{ result.thumbnail|safe }}" alt="{{ result.title|urlencode }} {{ result['favicon'] }}" />
         {% if result.content %}<p class="col-xs-12 col-sm-8 col-md-8 result-content">{{ result.content|safe }}</p>{% endif %}
     </div>
 </div>