Desktop: Enhance notelist focus behaviour

[miciasto]

This PR contains two enhancements to focus behaviour in the note list:

Focus following delete

1. Delete a note from the note list (eg using Delete key or context-menu)
2. Use Up or Down key to select the next note

Expected: the next note is selected, the user can continue navigating with the keys
Actual: nothing, the note list does not respond to the navigation keys anymore

Focus when navigating "away" from multiple-note selection.

1. Select multiple notes in the note list (eg Ctrl-A, or using mouse)
2. Use Up or Down key to select the next note

Expected: the next note is selected, and the previous notes are deselected
Actual: nothing, the note list does not respond to navigation keys anymore

This fix also fixes another issue discussed in forum as a side effect.

[laurent22]

Just need to fix the conflict and we can merge. (The "app" folder was removed so you will need to move your file one level down)

[miciasto]

I'm going to postpone this for now, until I get a chance to look at it.

It works for note delete, but breaks new note behaviour.

[miciasto]

Fixed and ready for review.

[tessus]

I'd like to merge this. Is there anything left to do? @laurent22 you already gave the ok to merge, but there were a few changes after your comment. Please advise.

[laurent22]

Looks good but I didn't test, however if you guys think it's ready to merge, please go ahead.

[tessus]

Oh, yes, I forgot to add the PR-tested label. I actually did test this.