You wouldn't believe what capability I'm adding to Perseus Zero!

Summary:
Adds a better default tag editor so that I don't have to
write one in perseus zero. This will give perseus zero
the ability to edit the raw tag keys, which is unreasonable
but not unreasonably so, since no one uses perseus zero
anymore.

This commit also fixes the unnecessary complaining about
EditorPage's ApiOptions prop.

Test Plan:
 * open localhost:9000/test.html
 * edit some "tags" on a group widget
 * check developer json mode for the tags

Auditors: joel