Add datetime tooltip to TLE age in new observation page

This commit also removes the display of the TLE set number
since it's useless for most satellites (data field has maximum value
of 9999).

network/templates/base/observation_new.html

@@ -2,6 +2,7 @@
 
 {% load staticfiles %}
 {% load tags %}
+{% load humanize %}
 
 {% block title %} - New Observation{% endblock %}
 
@@ -73,8 +74,10 @@
             {% for satellite in satellites %}
               <small class="tle" data-norad="{{ satellite.norad_cat_id }}">
                 {% if satellite.tle_no %}
-                  Using TLE set {{ satellite.tle_no }} issued
-                  {{ satellite.tle_epoch|timesince }} ago
+                  Using TLE fetched
+                  <span data-toggle="tooltip" data-placement="bottom" title="{{ satellite.tle_epoch|date:"Y-m-d H:i:s" }}">
+                    {{ satellite.tle_epoch|naturaltime }}
+                  </span>
                 {% endif %}
               </small>
             {% endfor %}