Listening to keyup instead of keydown for hotkeys & closing popup on releasing scan modifer key

[danpetruk]

Problem
Popup doesn't auto close when I stop pressing Shift (scan modifer key), which might be ok to someone, but is inconvenient for me.
I tried to change "configure keyboard shortcuts" settings and add Shift as close there, but this causes the popup to open and close back and forth.

Proposed solution
Change in this line in hotkey-handler.js keydown to keyup (and rename triggered function accordingly)
this._eventListeners.addEventListener(document, 'keydown', this._onKeyDown.bind(this), false);

I tried it locally and it works wonderfully and seem not to break anything.

Question
Would it be ok to submit pull request with such change?

[Kuuuube]

There is an existing setting intended for auto hiding the popup but it works a bit different. You can scan whatever then if you press the scan key again somewhere else with no text, the popup will disappear.

This setting could potentially be turned into a dropdown with something like None, KeyUp, and KeyDown. Or a sub-setting with KeyUp and KeyDown (similar to the Delay sub-setting).

You probably shouldn't submit a PR changing the hotkey behavior. But maybe it could be a setting somewhere.