support vcard RFC 6350 to track contact relaionships to other contacts

[nutpantz]

Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
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• This issue contains only one feature request.
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Feature description

https://www.rfc-editor.org/rfc/rfc6350#section-6.6.6

just needs a way to input the info into the app added
and link contacts to other contacts

Why do you want this feature?

as contact lists grow there is a real need to track contacts who are related to other contacts and how
the vcard standard has this implemented, but very few contact apps allow imputing this information
i cant remember the names of all the kids of my contacts, not even all the wives.
but its very helpful if i have the info handy, so it looks like i remember

Additional information

6.6.6. RELATED

Purpose: To specify a relationship between another entity and the
entity represented by this vCard.

Value type: A single URI. It can also be reset to a single text
value. The text value can be used to specify textual information.

Cardinality: *

Special notes: The TYPE parameter MAY be used to characterize the
related entity. It contains a comma-separated list of values that
are registered with IANA as described in Section 10.2. The
registry is pre-populated with the values defined in [xfn]. This
document also specifies two additional values:

  agent:  an entity who may sometimes act on behalf of the entity
     associated with the vCard.

Perreault Standards Track [Page 42]

RFC 6350 vCard August 2011

  emergency:  indicates an emergency contact

ABNF:

 RELATED-param = RELATED-param-uri / RELATED-param-text
 RELATED-value = URI / text
   ; Parameter and value MUST match.

 RELATED-param-uri = "VALUE=uri" / mediatype-param
 RELATED-param-text = "VALUE=text" / language-param

 RELATED-param =/ pid-param / pref-param / altid-param / type-param
                / any-param

 type-param-related = related-type-value *("," related-type-value)
   ; type-param-related MUST NOT be used with a property other than
   ; RELATED.

 related-type-value = "contact" / "acquaintance" / "friend" / "met"
                    / "co-worker" / "colleague" / "co-resident"
                    / "neighbor" / "child" / "parent"
                    / "sibling" / "spouse" / "kin" / "muse"
                    / "crush" / "date" / "sweetheart" / "me"
                    / "agent" / "emergency"

Examples:

RELATED;TYPE=friend:urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6
RELATED;TYPE=contact:http://example.com/directory/jdoe.vcf
RELATED;TYPE=co-worker;VALUE=text:Please contact my assistant Jane
Doe for any inquiries.

[Aga-C]

It's a duplicate of #90.