sort locations by label

The sorting happens between the BEFORE and the AFTER event. Templates
should generally use the BEFORE event to get their stuff properly
sorted, but they could use the AFTER event to add something to the start
or end.

helper.php

@@ -126,6 +126,7 @@ public function getLocations() {
         $data = array('' => $this->getLang('unknown'));
         $event = new Doku_Event('PLUGIN_TPLINC_LOCATIONS_SET', $data);
         $event->advise_before(false);
+        asort($data);
         $event->advise_after();
 
         return $data;