[fix] make /stats more CSP compliant - oscar theme

Replace oscar theme's *styles* (see below) by CSP compliant implementation in
``searx/static/themes/__common__/less/stats.less`` ::

    ./oscar/stats.html:29:  <th scope="col" style="width:20rem;">{{ th_sort('name', _("Engine name")) }}</th>
    ./oscar/stats.html:30:  <th scope="col" style="width:7rem; text-align: right;">{{ th_sort('score', _('Scores')) }}</th>
    ./oscar/stats.html:33:  <th scope="col" style="text-align: right;">{{ th_sort('reliability', _('Reliability')) }}</th>
    ./oscar/stats.html:38:  <td style="text-align: right;">
    ./oscar/stats.html:91:  <td style="text-align: right;"> {{ engine_reliabilities.get(engine_stat.name, {}).get('reliablity') }}</td>
    ./oscar/stats.html:109: <tbody style="padding-top: 1rem;">
    ./oscar/stats.html:112: <th scope="row" style="width: 10rem">{{ _('Exception') }}</th><td>{{ error.exception_classname }}</td>
    ./oscar/stats.html:114: <th scope="row" style="width: 10rem">{{ _('Message') }}</th><td>{{ error.log_message }}</td>
    ./oscar/stats.html:116: <th scope="row" style="width: 10rem">{{ _('Percentage') }}</th><td style="width: 10rem">{{ error.percentage }}</td>
    ./oscar/stats.html:121: <span style="border-right: 1px solid gray; padding: 0 1rem 0 0; margin: 0 0 0 0.5rem;">{{ param }}</span>
    ./oscar/stats.html:138: <th scope="col" style="width: 10rem">{{ _('Failed test') }}</th>

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


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