nav restructure

UK top nav:
Remove Science and Education

US top nav:
Remove Science

All editions:
Remove 'media' from secondary economy nav

UK sport:
Change Formula 1 to F1 in secondary nav
Add Racing (http://www.theguardian.com/sport/racing) to Secondary nav last

Culture, all editions
Add 'Classical' (http://www.theguardian.com/music/classicalmusicandopera) to secondary nav

All editions:
Add 'Media' as a main section in Meganav