[mod] infinite_scroll as preference

* oscar theme: code from searx/plugins/infinite_scroll.py
* simple theme: new implementation

Co-authored-by: Markus Heiser <markus.heiser@darmarIT.de>

searx/templates/oscar/base.html

@@ -100,6 +100,7 @@
     <script src="{{ url_for('static', filename='js/searxng.min.js') }}"
             data-method="{{ method or 'POST' }}"
             data-autocompleter="{% if autocomplete %}true{% else %}false{% endif %}"
+            data-infinite-scroll="{% if infinite_scroll %}true{% else %}false{% endif %}"
             data-translations="{{ translations }}"></script>
     {% for script in scripts %}
     {{""}}<script src="{{ url_for('static', filename=script) }}"></script>