Multiple fields for one attribute
    
    Current implementation has a limitation to have one field per one attribute. This is fine for most cases. For cases where an attribute can have two editor widgets which can be swapped a need for two different types of field may occur.
    
    This patch introduces 'param' option which supposes to contain attribute name. If 'param' is not specified it will contain field's name therefore backward compatibility is maintained. This extension allows to have two fields with different name and same param -> two fields get/supply value from/to the same attribute.
    
    Needed for:
    
    https://fedorahosted.org/freeipa/ticket/2372