Rebinding the universal.confirm keybinding currently doesn't make sense, because
the rebound key would also be used for editable prompts, which means you would
only be able to bind it to a ctrl key (not "y", which is desirable for some
people), and also it would allow you to enter a line feed in a branch name.
Fix this by always using enter for editable prompts.
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.
