[fix] make oscar theme more CSP compliant - default-image-style

Add default-image-style in::

    searx/static/themes/oscar/src/less/result_templates.less

Replaced style= in files::

    ./oscar/result_templates/default.html:19:        <img src="{{ image_proxify(result.img_src or result.thumbnail) }}" title="{{ result.title|striptags }}" style="width: auto; max-height: 60px; min-height: 60px;" class="col-xs-2 col-sm-4 col-md-4 result-content">
    ./oscar/result_templates/files.html:24:<img src="{{ image_proxify(result.img_src) }}" alt="{{ result.title|striptags }}" title="{{ result.title|striptags }}" style="width: auto; max-height: 60px; min-height: 60px;" class="col-xs-2 col-sm-4 col-md-4 result-content">

Reported-by: https://github.com/searxng/searxng/issues/57


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