Config report: preset the edit form to the current filter

The 'Username', 'Project Name' and 'Configuration Option' fields in the
'Set Configuration Option' form are now preset to the corresponding
value from the filter or defaulting to ALL_USERS, ALL_PROJECTS and blank
respectively if the filter is not defined or set to '[any]'.

This allows easier definition of related config, e.g. for a given
project or user.