Add additional validity states to the dictionary.nomenclatural_statuses table

[aazaff]

-- Sources taxa.nomenclatural_status_id. These are the legacy `opinions.status` values
-- that are neither an assignment nor a name change (12,806 legacy rows). The composite
-- UNIQUE (id, targeted) lets validity_opinions FK-pin (status_id, targeted) and enforce
-- "target_permid required iff targeted" as a plain CHECK (Way 2 / A1 / §10.6 D9).
CREATE TABLE dictionaries.nomenclatural_statuses (
    id integer GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
    status text NOT NULL,
    targeted boolean NOT NULL,  -- whether target_permid is required
    CONSTRAINT nomenclatural_statuses_id_targeted_key UNIQUE (id, targeted)
);
INSERT INTO dictionaries.nomenclatural_statuses (status, targeted) VALUES
    ('nomen dubium',        false),   -- legacy: 8,208
    ('nomen nudum',         false),   -- legacy: 2,533
    ('nomen vanum',         false),   -- legacy:   569
    ('nomen oblitum',       false),   -- legacy:    76
    ('informal',             false),   -- legacy: 18
    ('operational',          false),   -- legacy:  0
    ('invalid subgroup of', true);    -- legacy: 1,420

This is related to #46 and #26

[aazaff]

1. 'invalid subgroup of' now lives under the 'concept' tree in name_opinions. That is where it actually belongs, so it has nothing to do with this dictionary table or the validity_opinions table any longer.

2. Informal has been dropped from nomenclatural statuses. An informal name is simply nomen vanum.

3. Operational has been dropped from nomenclaural statuses. An operational name WILL be nomen utilis, but no logic yet exists for it. This issue exists to remind us that has to be added.