Implement accent insensitive search on directories for PostgreSQL

Currently the search on directories is case insensitive only (and always) and uses the ILIKE operator for PostgreSQL (or the LOWER ... LIKE for databases which does not support ILIKE operator).

This request is to provide a solution for people who wants to run accent insensitive queries on directories :

• on PostgreSQL, using the unaccent extension provides this capability
• on Oracle, using a specific collation should do the trick

So this ticket is to provide a solution for PostgreSQL only.