[UX] Improve importing keys

[str]

When importing the keys, the first field should be the private key, as once you paste it, it automatically populates the public key (2nd field). It is counterintuitive to paste first the last field. Also the warning about saving the generated private key can be put in the bottom, under the "copy" if the copy copies the private key. What does the "copy" button copy? It's not self explained, and if the user clicks anywhere outside the scatter, the scatter window closes, and the user is not able to return to that page.

It would be great if, after pasting the private key, both the public key as well as the account name in the mainnet are populated.

Also, the screen looks weird with so many font sizes.