Feature: Show the user that will be blocked before confirming

[Moe23333]

Show the user that will be blocked before confirming, and add a checkbox to choose users that don't want to block, it is helpful to avoid wrong blockings.

[cooljeanius]

Show the user that will be blocked before confirming, and add a checkbox to choose users that don't want to block, it is helpful to avoid wrong blockings.

Additionally, if adding this feature, it'd be useful for the add-on to remember how the user confirmed (or not) previously, so you don't end up blocking someone you already decided you didn't want to block in a previous chain-block