Password policy measurement units.
    
    When filling password policy it may be unclear what value to enter because user may not remember field's measurement unit.
    
    This patch adds support for declaring measurement units. It's done in field's/widget's spec by entering key for unit's string (which is in IPA.messages.measurement_units[key]).
    
    Measurement units in table layout are displayed in parenthesis after label. It is to be consistent with some fields which have measurement unit integrated in label.
    
    This patch defines measurement units for password policy's 'History size', 'Failure reset interval' and 'Lockout duration' fields.
    
    https://fedorahosted.org/freeipa/ticket/2437