Revert "contrariamente a quanto dicono nella documentazione, si può fare spacchettare tutto nella stessa directory, senza creare una directory wp/ per core"

Si può fare, ma se viene fatto un update di wordpress core poi si perdono tutti i temi/plugin/etc.

Ho cambiato leggermente la struttura delle directory generate, ed ho spiegato tutto dentro README.md

This reverts commit 19f27161.

- moved themes related patches to patches/themes (yet to check)
- moved wp core patches to patches/core
- split the mega-patch for hyperdb in the individual edits. I removed the one related to nextgen-gallery since I think it is not relevant anymore (but I might be wrong)

I am still not sure if we want to use Composer to manage the
dependences of r2db, which is only flexihash. It might be easier to
simply add flexihash to the repository of r2db, which we never have
updated in 7+ years. That way we would not need to include the vendor/
folder into the Noblogs production enviroment.