Update Config.groovy

1. Corrected typo in line 118 "grails.plugin.springsecurity.ldap.search.filter" (was ".fliter").
2. Fixed typo in line 28 ("Lucene" - was "Lucane")
3. Fixed spelling of "PostgreSQL" in line 37 (was "PostgresSQL" - see www.postgresql.org for confirmation)
4. Various minor clarifications in comments