[feature] keyboard navigation support (suggested only for sortables with handles)

[ARitz-Cracker]

Is your feature request related to a problem? Please describe.
Things cannot be moved around with keyboard navigation.

Describe the solution you'd like
A relatively simple and easy solution seems to be:

1. Set the tab-index to all elements which match the optional class specified in the "handle" option set to 0 allowing it to be focus-able with tab navigation.
2. Add a keypress event listener on the handle which can move the thing with up/arrow keys.

Describe alternatives you've considered
I may create my own npm package which facilitates this, though it would be useful to have this upstream.

Additional context
I'm primarily creating this issue wondering, if I where to submit a PR for this feature, would it be merged?