Cache for VC Statistics #801
Description
VC list web-service includes statistics which still requires a long time (ca. 6 minutes) to compute for all corpora including those from C2 (W1 gesamt). Thus, the statistics should be cached when a Kustvakt server is started.
Since we allow updating index on the fly via closing index reading web-service, the statistics should also be updated. We probably need a web-service to update VC statistics.