Desktop: Support "select all" in the note list

[miciasto]

Please consider this PR for enhancing the "select all" function in Joplin.

As mentioned in forum

Spec

• When focus is in the note list, "select all" selects all notes.
• When in the folder list, "select all" does nothing.
• When in the tag list, "select all" does nothing.
• The key combination "select all" is "Ctrl-A" or "Cmd-A"

For reference, the current behaviour is this:

Tests

• Add unit test for new "NOTE_SELECT_ALL" handler in reducer

Manual tests:

Check 'select all' works:

• in note list (selects all notes in note list)
• in tag list (does nothing)
• in folder list (does nothing)
• in note text (still works and is unaffected)

Discussion

If the note list is short, and "select all" is actioned below the last note, the application menus are selected. I would like to stop this too, but don't know where to catch it. So leaving it as is for now.

[laurent22]

I didn't test, but the code looks good and there are test units, so let's merge! Thanks for the quality pull request @mic704b!

[miciasto]

Thank you @laurent22