Column items which are None are rendered as an HTML comment, and will appear in the UI as a blank.

…vements

Do not render None in columns

Endpoint serves as a way to delay a call to `url_for` in a common pattern,
as well as provide .active and .enabled attributes where appropriate.

EditColumn -> ActionColumn, which can also accept a static label and so becomes appropriate both for linked contents, and for action buttons at the end of table rows.

Groups CSS and JS files and provides them via dominate tags to render consistently and easily.