feature: List “static pages” in the right-hand column.

This lets the administrator designate some entries as “static pages” which exist outside the normal article flow. Instead, they are linked directly from the right-hand column (where there isn't a lot of room for long page titles).

To make an entry a “static page”, pretend that it is published in the year 1900. All entries associated with the year 1900 will be listed as “static pages” in the right-hand column, in the order of their “publication date”. Normal users get to see static pages in their designated language only; administrators see all static pages.

This is a hacky solution but it saves us from having to duplicate the editing/publication mechanism.