Settings should be closable in sub-pages with escape key

[Simon Laux]

Or go back first to main settings page and then close on the second press, I assume.

[bjoern]

and then close on the second press, I assume.

yip, the "Esc"-key should hit the topmost's dialog "back button"

and if if there is none, close the topmost dialog

[Max Philippov]

Is #2268 related? In terms of "we need to manage how dialogs are stacked and which one is closed by ESC". I can take that after resolving more pressing bugs since I'm reworking Dialog as part of BlueprintJS removal