F docs reorganize

I reorganized the chapters under "Specification", such that the parts that are likely to be interesting to users are further up. Furthermore, I renamed some of them.

Remove the dropbox, since we want to drop support for it

I think people expect stuff like what is given under Entity API when they read this. I would like to rename it to prevent confusion.

Reordering to have the interesting stuff at the top

Everything is API Spec :-D

I think this is clearer.

assigned to @henrik