Make sure status colors CSS is available

[dregad]

Starting with MantisBT 2.26.0, status_config.php (dynamic CSS for status colors) is no longer systematically loaded by core.

This results in linked issues' status icons on the plugin's View page, to be shown in black instead of the appropriate color, as shown in screenshot

The stylesheet has to be loaded by individual pages that need it (see issue #30773, mantisbt/mantisbt#1833)