core: rework the confirmation spawn prompt

core: rework the confirmation spawn prompt

Previously it was "[Yes, Fail, Skip]" which is pretty misleading because it
suggests that the whole word needs to be entered instead of a single char.

Also this won't fit well when we'll extend the number of choices.

This patch addresses this by changing the choice hint with "[y, f, s – h for help]"
so it's now clear that a single letter has to be entered.

It also introduces a new choice 'h' which describes all possible choices since
a single letter can be not descriptive enough for new users.

It also allow to stick with the same hint string regardless of how
many choices we will support.