Add option to filter launches by orbit

templates/launches.html

@@ -39,6 +39,21 @@
   {% endfor %}
   </p>
 
+  <p>Orbit:
+  {% if request.args.orbit %}<a href="{{ request.path }}">🗙</a>{% endif %}
+
+  {% for name, abbrev in orbits | sort %}
+      {% if abbrev == request.args.orbit %}
+        <strong>{{ name }}</strong>
+      {% else %}
+        <a href="?orbit={{ abbrev }}" class="text-nowrap">
+        {{ name }}
+        </a>
+      {% endif %}
+      {% if not loop.last %} | {% endif %}
+  {% endfor %}
+  </p>
+
   {% for launch in launches %}
     {% set highlight =" bg-primary-subtle" if launch.slug in config.FOLLOW_LAUNCHES else "" %}
     {% set country = get_country(launch.country_code) %}