Fix osname ownership check UI

[0x70b1a5]

Problem

• When a user is registering an osname, there's no message in the UI if a name is already claimed.

Solution

• Our ethname hashing library is out of date, switch to a working fork under a different organization (@ensdomains)
• Polyfill node Buffer to make the above work in-browser

Testing

• In a new node, try to register an existing name
• Confirm the "Name is already claimed" message displays
• Try to register an unclaimed name
• Confirm you can start up the new node as expected