Added support for defining override sections for fields in the relationships.ini file.  The syntax is
[relationshipname.fieldname]
   visibility:list=hidden
etc..
2 new methods added to Relationship to support this.  getFieldDefOverride() and setFieldDefOverride().  Currently only the RelatedList uses this to check for visibility overrides but we can expand this to the advanced find form and other aspects of the application as well.
Also added utility method df_get_from_struct() that allows us to get deep attributes from a PHP structure without worrying about null parents.  It uses a path notation like a:b:c