This complements 7f877621 (Move wendelin.core from Wendelin to ERP5) for
wendelin.core 2 which introduces new filesystem server component that serves
in-ZODB arrays data as OS files for Zopes to memory-map.

- WCFS is by default disabled in ERP5 - we do not want to load every
  ERP5 user with it in the early days of wendelin.core 2.
- WCFS is by default enabled in Wendelin and SlapOS Master.
- There is a duplication for instance-erp5.cfg.in in between stack/erp5/
  and software/slapos-master/ . It was negotiated with VIFIB developers
  to go this way instead of first deduplicating instance-erp5.cfg.in
  copying that was started in 87d13789 (slapos-master: Copy files from
  erp5 stack for local changes).