Support ed25519 ssh keys

[denics]

Is your feature request related to a problem? Please describe.
It is more and more common to use ed25519 keys to connect via ssh to out devices but, when I try to add a ed25519 key at https://account.mycroft.ai/devices/ I get an "Invalid RSA public key format" which is ok, because you do not support ed25519 😄

Describe the solution you'd like
It should be fairly easy to support ed25519

Describe alternatives you've considered
An inconvinient alternative is to create an alternative key and use that with the -i option in ssh

[krisgesling]

Thanks for flagging this - we'll take a look at what's required.

[LiberalArtist]

I suspect this is really an issue with the web UI: OpenSSH has supported ed25519 since version 6.5 (released in 2014). I haven't tried it, but I think it might be possible to add an RSA key via the web UI, use it to SSH into the device, and then manually add a ed25519 authorized key.