Sort legacy-compatible menu items

This imposes a consistent order: menu weight first, alphabetically
second sort key. That way, it no longer matters in which order the
file system reports the files (which is different between machines).

The issue was reported out by Christophe Leterrier.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add separators before legacy-compatible menu items

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>