Additional.lyx: subsections 10.8, 10.9 and 10.10

[Jean-Pierre Chrétien]

Dear doc maintainers,

While updating the translation of the French Additional.lyx manual, I saw that 
in the original manual these three subsections, which were previously in a 
section entitled "Lyx Features needing Extra Software", appear now in section 
"The lyx Server".
This mistake was introduced with commit 7b447915c2464effea8bae1c0701745fbc30ea5f

I restored chapter 11 as before.

-- 
Jean-Pierre