Lucene indexing of mv facets fails because of hidden persisted FacetsConfig

When performing (re)indexing of a multi valued property that's used for facets, indexing fails because the :facets-config node is hidden and therefore after first indexing any subsequent diff fails at seeing it because the VisibleEditor doesn't traverse nodes starting with :.
The solution is to use a not hidden node name for multi valued facets config (stored in NodeStateFacetsConfig).