[Expo] (Minor) Move a function definition.
[Expo] Unify key-press and key-release handling.
[Expo] Implement keyboard-controlled gradual zoom.

Ctrl+'+' (plus): Increase the zoom level.
Ctrl+'-' (minus):  Decrease the zoom level.
Ctrl+'0' (zero): Exit zoom.
[Expo] Handle more keyboard events on key-release instead of on key-press.