Allow Users to Tab Through Hues

[foohyfooh]

-Change the click event handler to focus event handler and add a tab index to the hue divs to allow a user to tab through the hues. -Get focus back on the selected hue after the user selects a colour or uses the context menu so that when the user presses tab again it will move to the hue after the selected one.

[romannurik]

Hey there! Thanks for the PR. I'm a little hesitant on this because I'm actually hoping longer-term that the entire window isn't focusable (there's a FR w/ the electron project for that). Another solution for switching hues is a set of global hot keys, that I think is worth exploring soon.

[foohyfooh]

If I understand correctly, it would using globalShortcut (https://github.com/electron/electron/blob/master/docs/api/global-shortcut.md) to listen for the tab key or do you have a different key combination in mind?