fix: Relates to #324. Show link to Blockscout upon confirmed, not the first confirmation

[ltfschoen]

To overcome situations when we don't receive any sendStore.confirmations for a long time after it txStatus.confirmed key is set (i.e. situations when sendStore.confirmations jumps from a value of say -1 to a high value which corresponds to a long delay waiting without the user knowing what's going on), we'll make sure we provide a link to the Blockscout transaction as soon as txStatus.confirmed key is set, because at the moment it only shows the link after confirmations >= 0, but the value of confirmations may stay at a negative number for a long time.

Now what happens is:

1. txStatus is signed, then it shows "Sending your transaction..."

2. txStatus.confirmed key is set, but sendStore.confirmations is often a negative number, so:

• Title: 'Submitted' https://github.com/paritytech/fether/blob/master/packages/fether-react/src/Send/Sent/Sent.js#L127
• Description: 'Waiting for confirmations...' https://github.com/paritytech/fether/blob/master/packages/fether-react/src/Send/Sent/Sent.js#L95

Previously it still didn't show a link to Blockscout, because it would still be waiting for confirmations >= 0 even though the transaction would be available on Blockscout.

In this PR we now show the Blockscout link to the transaction as soon it txStatus is confirmed.

3. sendStore.confirmations will often jump to a positive number and change to displaying say "Waiting 3/6 confirmations", since the logic in Sent.js is such that the minimum confirmations is set to a constant of 6 before it displays "Transaction confirmed"

4. Finally when minimum confirmations >= 6 it shows "Transaction confirmed", but sometimes sendStore.confirmations may be say 3 when at the Blockscout link it says its already up to say 15 block confirmations!

In this PR I've added extra padding between the title and the link to Blockscout

[Tbaut]

Sure, that's makes the UX better without changing much to the code. I don't mind the padding as well 👍