add upload hotkeys: n & shift+n

[juodumas]

Upload process before: 1) click up2k icon; 2) click upload; 3) click files or folder in modal
Upload process after: press N
Or do you all drag & drop?

Hotkey is N because it is opposite of Y and can also stand for (N)ew.

This PR complies with the DCO; https://developercertificate.org/

[9001]

a huge inconvenience with initiating an upload by clicking the upload-button (and/or with this hotkey) is that it initiates file selection using a more restricted API than a drag-drop would;

the webbrowser has security features which prevents the javascript from recursing into a selected folder if it comes from the click-to-upload action,

so the only way to upload a folder and all its subfolders is by dragdrop; can't be done with the button

so I'm not really sure if this is worth it , but i'll keep it open for now -- figured i'd say something at least

[juodumas]

Thanks. Then let's add only the file upload shortcut and skip the folder upload shortcut? I don't use drag & drop uploads and three mouse clicks to upload is a pain.