Milestone Network code

We now have checksum and lengths for all objects after metalink download:

Pass in name/url/checksum/len/etc. Have backend fail early if we go over our given length.

Integrate presto, do presto like stuff for metadata (not just packages).

Add APIs to allow async downloads of multiple objects.

Ability to share downloaded data over local network, avahi etc. -- needs integration with presto, and a real server to be written)

Dynamic fastest mirror instead of basing everything on one connect().

Make sure spacewalk works.