Allow empty fields in create Account UI. Refs #1763

Network address and mask are optional. Fixed also the AccountType and
User fields validators.
Force Account table reload after mutation request. #1763

Workaround for LazyLoaderAdapter: too lazy to reload values after we
have changed DB values through direct DatabaseInterface calls!
Removed IPsec client configuration. Refs #1763 #1957

IPsec "client" configuration is still not supported: we accept L2TP
roadwarriors only.