keybindings: get Qt to display keyboard shortcuts
I think it will DTRT on macOS, but we should be careful not to save the
results to disc (per Qt docs). I expect its going to write clover-leaf instead of
Ctrl
on that platform. This Fixes #947 (closed) and Fixes #2244 (closed).
Need: someone to look at the resulting artifacts on mac. Except macOS artifacts might be broken at the moment...