Remove requirement for private key

[amanusk]

I think the tool could be improved and more easily recommended if there was no need to put in the private key.
The target demographic are the ones who have been burned by pasting their private key in the wrong place.

A possible solution is to:

1. Sign a Tx with the compromised Private key (e.g. only a single PK is imported to MM)
2. Change the account to one that is not related to the compromised seed to pay for the gas

So this would require to connect the wallet twice, once with the compromised account and once with a safe account.

Not the best UX, but arguably better than pasting a private key.

[kendricktan]

Unfortunately that is not possible on metamask MetaMask/metamask-extension#2506

I really wanted that to work but for now you need the actual private key :\