[fix] paging for api forms

searx/templates/results.html

             <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>
             <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>
             <div class="">
             <input type="hidden" name="q" value="{{ q }}" />
             <input type="hidden" name="format" value="rss" />
+            <input type="hidden" name="pageno" value="{{ pageno }}" />
             <input type="submit" value="rss" />
             </div>
         </form>