Expose SSH public key to client

[dwosk]

The desktop app generates a unique SSH private key on startup. The corresponding public key is made available in the get_info RPC API, which can be used by downstream apps to register the key with any HSTS that supports SSH authentication with unique private keys.

[dwosk]

        asperaDesktop.getInfo().then(appInfo => {
          console.log('SSH PUBLIC KEY', appInfo.client_pubkey);
          console.log('VERSION', appInfo.version);
        }).catch(error => {
          console.log('GET INFO FAIL', error);
        })