make KorAP instance configurable

see example.conf

Change-Id: Ia6ece608272cf21efba29e23f948434164487f3d
diff --git a/example.conf b/example.conf
index cf8a324..4991015 100644
--- a/example.conf
+++ b/example.conf
@@ -13,7 +13,8 @@
   },
 
   w2v => {
-    vecs => "example-models/wpd19_10000/wpd19_10000.vecs"
+    vecs => "example-models/wpd19_10000/wpd19_10000.vecs",
+    # korap_url => "https://korap.ids-mannheim.de"
   },
 
   downtime_calendar_url => "https://cloud.ids-mannheim.de/remote.php/dav/public-calendars/QfRCG4HriLcZJJRd?export",