Add BASE_URL constant to page and have AJAX calls use it

public/assets/admin/js/admin.js

@@ -2,15 +2,3 @@
  * admin functions, mostly map/mapping related
  */
 
-function phpvms_vacentral_airport_lookup(icao, callback) {
-    $.ajax({
-        url: '/api/airports/' + icao + '/lookup',
-        method: 'GET',
-        headers: {
-            'x-api-key': PHPVMS_USER_API_KEY
-        }
-    }).done(function (data, status) {
-        callback(data.data);
-    });
-}
-