As program manager I want to edit links on program items and schedule items

Most links are program item level, but sometimes we may need to put them on schedule item, eg. schedule items of program may have different signup links.

Under the hood, links are stored in annotations: `internal:links:signup` is the signup link and `internal:links:signup:title` is an optional title for it.

There is even an option for localized links: `internal:links:signup:fi` (and `internal:links:signup:fi:title` or `:title:fi`?)

But 95% of the use case would be covered by un-localized links on Program Item.