Register handler for Zeronet (`zeronet:`)

Has Zeronet an URI scheme defined ?

I don't seem to have anything register on my system. Could be a nice feature to have. It would behave like magnet link for Bittorrent and start zeronet automatically when clicking on a `zeronet:ADDRESS` link.

No files, tests, or entry points are named. Start by locating how ZeroNet is launched and how platform integrations are handled; define the supported scope for a `zeronet:` URI handler and verify that clicking such a link starts ZeroNet with its address.

索引モデルが issue の本文から書いたものです。