#139 Move table and field comments from the Wiki to the database

[Ahasuerus]

Move all MySQL table and field comments from the ISFDB Wiki (http://www.isfdb.org/wiki/index.php/Database_Schema) to the database.

For MySQL tables the syntax is:

ALTER TABLE authors COMMENT = 'my comment';

Adding a coment to a column definition requires repeating the complete column definition as per
https://dev.mysql.com/doc/refman/5.5/en/alter-table.html:

ALTER TABLE t1 MODIFY col1 BIGINT UNSIGNED DEFAULT 1 COMMENT 'my column'