Refactor: add a separate Prompt view

So far, confirmations and prompts were handled by the same view, context, and
controller, with a bunch of conditional code based on whether the view is
editable. This was more or less ok so far, since it does save a little bit of
code duplication; however, now we need separate views, because we don't have
dynamic keybindings, but we want to map "confirm" to different keys in
confirmations (the "universal.confirm" user config) and prompts (hard-coded to
enter, because it doesn't make sense to customize it there).

It also allows us to get rid of the conditional code, which is a nice benefit;
and the code duplication is actually not *that* bad.

pkg/cheatsheet/generate.go

@@ -116,6 +116,7 @@ func localisedTitle(tr *i18n.TranslationSet, str string) string {
 		"commitDescription": tr.CommitDescriptionTitle,
 		"commits":           tr.CommitsTitle,
 		"confirmation":      tr.ConfirmationTitle,
+		"prompt":            tr.PromptTitle,
 		"information":       tr.InformationTitle,
 		"main":              tr.NormalTitle,
 		"patchBuilding":     tr.PatchBuildingTitle,