ToDo list for khard

1. Add support for vcard attributes kind and member
    - kind column in contact table
    - option to filter contact table (--kind)
    - member action to list all members of an organisation

2. Structure of fn attribute should be customizable in contact editor
    - For example (vars in {} are placeholder):
        [...]
        full name : {last}, {first} {additional}
        [...]
    - additional parameter for --display option "full_name"

3. Implement impp attribute, see #105 for more information

