More bandwidth efficient download of Veloren

[Songtronix]

Right now Airshipper just downloads the zip everytime which includes all assets. This should be avoided by unzipping it to the s3 storage with a file list and hashes for the client to check each file and the hash locally, downloading what's corrupted, missing, outdated.

For the hashes we can use: https://mvdnes.github.io/rust-docs/zip-rs/zip/read/struct.ZipFile.html#method.crc32 Probably follow this workflow for robust updating: https://github.com/ioquake/ioq3/blob/master/autoupdater-readme.txt