Added multi-valued text widget.
    
    A multi-valued text widget has been created to replace the old
    IPA.details_field. The old code was designed to handle all data
    types, and it uses one <dd> tag for each value, so the code is
    still incomplete and complex. The new code was designed to handle
    only multi-valued text attributes, and it uses one <dd> tag for
    all values, so it's easier to maintain. There are already other
    widgets that can be used to handle other data types.
    
    The new code supports line-level undo and line-out for removal
    like the old code, but there are some changes:
     - Undoing a newly added line will remove the entire line.
     - Editing the value of a removed line will cancel the removal.
     - It provides 'undo all' link to reset the entire attribute.
    
    The old code will be cleaned up in a subsequent patch.