improved keybindings

- home & end no longer do the windows-y nonsense of jumping to the ends
of the current line
- moved jump-to-line to ^G to make room for a joinLines command at cmd-J
exports now display every frame

- rather than just updating the view once per `batch’.
updated key equivalents
ditched the `status` toolbar

- the zoom slider wasn’t very useful anyway (beachballs if the script
takes any significant time to render)
- the export progress spinner now lives in the title bar
- roll over the spinner to reveal a Cancel button
- also: switched the SplitViews to hairline dividers (so modern…)