Keyboard shortcut for selecting/de-selecting tabs

[heywoodlh]

It would be awesome if you could select/deselect tabs using keyboard shortcuts. It almost defeats the purpose of having keyboard shortcuts for splitting tabs if you aren't able to keep things on the keyboard. (However, I love this feature and want to be clear I'm very grateful for it! 😄)

The way I would imagine this working is that if you press the keyboard shortcut to add a tab to your selection it would add the tab directly below the one you are currently on and if you press the keyboard shortcut to remove tabs would cycle the opposite direction. I'm not a UX person at all, so maybe this wouldn't be ideal.

This would be related to #748 but I didn't find other discussions that covered this specifically.