Add contact types table, web API

In the user JSON schema there is a property named preferredContactType which contains a numeric value. The values appear to be hard-coded and there is no lookup table for it.

Please add a table along the lines of

CREATE TABLE diku_mod_users.contact_types (
    id VARCHAR(3) NOT NULL,
    name VARCHAR(128) NOT NULL,
    PRIMARY KEY(id)
);
INSERT INTO diku_mod_users.contact_types VALUES ('001', 'Mail'),  ('002', 'Email'),  ('003', 'Text message');

And a web API such as /contact-types to query the values.

Also consider changing the ids to UUIDs as is requested in MODUSERS-123. If nothing else, it would be useful to have a lookup table for the contact types, even if it only contains static values.