Smarter Download Button

[lidel]

Right now Download always downloads .tar archive with all shared files.

This is cool for directories and multiple files, but annoying when a single file is shared.
In that case there is no need to wrap single file in an archive – user should fetch it directly.

I think we should detect when only one file is shared, and make it either (TBD):

• do the download via ipfs.cat
• link to it directly with https://ipfs.io/ipfs/{cid}?filename={name}&download=true parameter, which will trigger download via content-disposition HTTP header
  • I've added it in feat(gateway): Content-Disposition improvements ipfs/kubo#7677 – will ship in go-ipfs 0.8.0, but is already running on our gateway so safe to use.