Offer default values for new ISP settings

That is to be backward compatible, avoiding to break the HTML of existing
installations on update.

ref #34, #33

wifiwithme/apps/contribmap/templates/base.html

@@ -30,7 +30,7 @@
     <div class="container">
     <h1>
     {% block title %}
-    <a href="{% url 'home' %}">{{ isp.TITLE }}</a>
+    <a href="{% url 'home' %}">{{ isp.TITLE|default:"Réseau wifi expérimental" }}</a>
     {% endblock %}
     </h1>
     </div>

wifiwithme/apps/contribmap/templates/contribmap/wifi-form.html

@@ -82,7 +82,7 @@
       <div class="form-group col-sm-6">
         <div class="form-group form-group-lg form-inline">
           <input type="text" name="search"
-                 id="search" placeholder="{{ isp.ADDRESS_EXAMPLE }}" class="form-control" />
+                 id="search" placeholder="{{ isp.ADDRESS_EXAMPLE|default:"rue du calvaire, nantes" }}" class="form-control" />
           <span id="search-btn" class="btn btn-default btn-lg" data-loading-text="...">Recherche</span>
 
           <div id="search-results" class=""></div>