Quit if system clock is wrong

[jurijus01]

Is your feature request related to a problem? Please describe.
Spent few hours on Discord getting help about peculiar edge case when block sync approached 93% and then started decreasing, having 2-3 peers connected and trustedNodeSync also worked. Much confusion and analysis all to find out that the system clock was set wrong in the end! My node was rejecting any new blocks and rejecting any peers that would serve up-to-date blocks treating the blocks ahead of my clock as "impossible scenario"....

Describe the solution you'd like
Wouldn't it be great if Nimbus client on startup could:

1. get Internet Time from a time server (or few);
2. compare Internet Time to the system clock;
3. if system clock is out of sync with Internet time, quit with message "Please correct your system clock!"