Refine UI layout

As suggested/reported by Joe F (mergesort):

• He’s not keen on the overall alignment and organisation of all buttons/inputs (it’s true that in certain states there’s a lot of icons, they have no hover states, and perhaps they’re not grouped effectively enough).

• Joe would prefer a more standard left aligned prompt field, he doesn’t like the way it needs to slide while you type. This is fair enough, we should implement this at the very least as an option.

One small thought of my own: could group settings button with model picker, since it’s settings-y. (I don’t think we should remove the settings button entirely since many people don’t even realise the menu bar icon exists).