Files in manifest - to be merged *after* the master-pull-request

This changes freesite inserts to put the smallest files into a container, up to 2 MiB.

It starts with the smallest files referenced from index.html and includes all files which fit in 2 MiB. Then it checks whether further unreferenced files fit into 2 MiB. The rest of the files are uploaded as separate files as before (CHKs).

For graphic-heavy freesites like Freenet_Meltdown, this can reduce the site load time by more than factor 3.