[fix][#36] remembering results download categories

        <div id="apis">

        {{ _('Download results') }}

        {% for output_type in ('csv', 'json', 'rss') %}

        <form method="post" action="/">

            <div class="left">

            <input type="hidden" name="q" value="{{ q }}" />

            <input type="hidden" name="format" value="csv" />

            <input type="hidden" name="pageno" value="{{ pageno }}" />

            <input type="submit" value="csv" />

            </div>

        </form>

        <form method="post" action="/">

            <div class="left">

            <input type="hidden" name="q" value="{{ q }}" />

            <input type="hidden" name="format" value="json" />

            <input type="hidden" name="pageno" value="{{ pageno }}" />

            <input type="submit" value="json" />

            </div>

        </form>

        <form method="post" action="/">

            <div class="">

            <input type="hidden" name="q" value="{{ q }}" />

            <input type="hidden" name="format" value="rss" />

            <input type="hidden" name="format" value="{{ output_type }}" />

            {% for category in selected_categories %}

            <input type="hidden" name="category_{{ category }}" value="1"/>

            {% endfor %}

            <input type="hidden" name="pageno" value="{{ pageno }}" />

            <input type="submit" value="rss" />

            <input type="submit" value="{{ output_type }}" />

            </div>

        </form>

        {% endfor %}

        </div>

    </div>