Nano Setup - Add check that user really noted the Index

[CrashTD]

Description

Adding a check to the setup process, comparable to the one used for the seed to make sure the user wrote down the Index Number. So asking the user to reenter the Index and check if its correct.

Motivation

The last few days in the help channel and on Reddit I noticed that when people restore their Trinity accounts they regularly don't know which index they used.

While Trinity points out that the index should be written down, an additional check would ensure it.

Although most people choose an index of 0 or 1, the danger that someone chooses a higher one and forgets it and then has no access anymore exists. And brute forcing through all 2147483648 possibilities would be a task for 2 lives.

Am I planning to do it myself with a PR?

No.