Changed buildUniqueExclusionRules to search for 'unique:' rather than 'unique' so that custom rules are not changed

1. Fixed Mixed tabs and spaces in this file.
2. Updated buildUniqueExclusionRules so that it searches for 'unique:' rather than just 'unique'

Example (see https://github.com/felixkiss/uniquewith-validator)
This Rule:
'unique_with:traffic_groups,document_id'

Was being changed to:
'unique:traffic_groups,document_id,1,id'

but should not have been changed at all because it is custom