The Factorio Mod Portal uses and provides SHA1 hashes of mods, so it
makes sense to align the ModPack and ModInfo structures to sha1 by
renaming the genericly named hash property to sha1.
Add ModPack data type with corresponding storage on the master, messages
to create, update and delete them, as well as commands to invoke them.
The ModPack data type contains a list of mods with versions and optional
sha1 hashes, and mod settings to be used.
Add the ability to manage a set of mods to be shared by the master
server to the rest of the cluster. This implements storage, uploads,
downloads, deletetion, and listing details of mods but does not actually
do anything with the stored mods.