Web interface with map where user can place pin for testing

Closes: #21

templates/index.html

@@ -16,6 +16,8 @@ Wikidata Query service (WDQS)</li>
 <li>Return the most specific Wikidata QID and Commons Category.</li>
 </ol>
 
+<p><a href="{{ url_for("map_page") }}">Interactive map with clickable pin for geocode testing</a>: click on any location within the map to place a pin and see the geocoding results for that specific point.</p>
+
 <form>
 Latitude/Longitude: <input name="q"/> (e.g. 54.375, -2.999) <input type="submit" value="go"/>
 </form>