oscar template: update messages

searx/templates/oscar/messages/first_time.html

+<div class="alert alert-info fade in" role="alert">
+    <button class="close" data-dismiss="alert" type="button">
+        <span aria-hidden="true">×</span>
+        <span class="sr-only">Close</span>
+    </button>
+    <strong class="lead">{{ icon('info-sign') }} {{ _('Heads up!') }}</strong>
+    {{ _('It look like you are using searx first time.') }}
+</div>

searx/templates/oscar/messages/js_disabled.html

 <div class="alert alert-warning" role="alert">
-    <strong>{{ _('Warning!') }}</strong>
+    <strong class="lead">{{ _('Warning!') }}</strong>
     {{ _('Please enable JavaScript to use full functionality of this site.') }}
 </div>

searx/templates/oscar/messages/no_data_available.html

+{% from 'oscar/macros.html' import icon %}
+<div class="alert alert-info fade in" role="alert">
+    <strong class="lead">{{ icon('info-sign') }} {{ _('Heads up!') }}</strong>
+    {{ _('There is currently no data available. ') }}
+</div>

searx/templates/oscar/messages/save_settings_successfull.html

+{% from 'oscar/macros.html' import icon %}
 <div class="alert alert-success fade in" role="alert">
     <button class="close" data-dismiss="alert" type="button">
         <span aria-hidden="true">×</span>
         <span class="sr-only">Close</span>
     </button>
-    <strong>{{ _('Well done!') }}</strong>
+    <strong class="lead">{{ icon('ok-sign') }} {{ _('Well done!') }}</strong>
     {{ _('Settings saved successfully.') }}
 </div>

searx/templates/oscar/messages/unknow_error.html

+{% from 'oscar/macros.html' import icon %}
 <div class="alert alert-danger fade in" role="alert">
     <button class="close" data-dismiss="alert" type="button">
         <span aria-hidden="true">×</span>
         <span class="sr-only">Close</span>
     </button>
-    <strong>{{ _('Oh snap!') }}</strong>
+    <strong class="lead">{{ icon('exclamation-sign') }} {{ _('Oh snap!') }}</strong>
     {{ _('Something went wrong.') }}
 </div>

searx/templates/oscar/stats.html

                 {% endfor %}
                 {% if not stat_category %}
                 <div class="col-sm-12 col-md-12">
-                    <div class="alert alert-info" role="alert">
-                        {{ _('There is currently no data available.') }}
-                    </div>
+                    {% include 'oscar/messages/no_data_available.html' %}
                 </div>
                 {% endif %}
             </div>