Add host discovery to authentication page

Find all domains for a given hostname.

refs #6093

Conflicts:

	application/forms/Install/AuthenticationPage.php
Move dns discovery functions into separate class

Add functions to lookup and reverse-lookup domain names and move the ldap
discovery function into a separate class

refs #6093
Merge branch 'feature/ldap-discover-by-dns-6093'
Detect ldap default naming context

Read the entries in the RootDTS of the given ldap server, to discover
its default naming context and capabilities

refs #6097
refs #6096
Merge branch 'feature/ldap-get-naming-contexts-6097'