add activists.pronouns column

[mdempsky]

This commit adds a pronouns column to the activists table. This includes additional wiring for all of the CRUD operations relating to it, copy/pasted from handling of the phone column.

Notably, there's already a 20-character pronouns column in the form_application table; evidently, it originally existed but was removed in mid 2019. For simplicity, I kept the 20-character limit.

Per Cassie's request, this is a free-form text box.

Existing ADB SQL databases can be migrated by running:

ALTER TABLE activists ADD pronouns VARCHAR(20) NOT NULL DEFAULT '';