Summer school preparations (including important changes in nestedMenu)

A quite incoherent PR that contains various fixes and updates uncovered while preparing for the Leipzig Summer School.

Apart from configuration updates to the Perseids confs and the SG labelset, the important thing here are the changes made to the `nestedMenu` directive, which now at least correctly notifies the saver that something changed - not a final solution, but will work in the interim.

45058f1 is really important, as it provides a huge speed-up to the directive.