Removing Esc as a quit key

[thutt]

There have been a few complaints about using 'Esc' as a key to quit the view-review-tabs program. The main complaint being that accidentally pressing 'Esc' is cumbersome if URL-based diffs are being used, and the web server requires credentials for access -- because the credentials have to be provided again.

Although that particular problem is mitigated by using the host OS keyring to store credentials, 'Esc' is non-standard. So, it's best to remove it.

The way to quit the program now is more standard: Ctrl-Q.