first pass of keyboard support

[nelsonpecora]

• adds tabindex="0" to the labels, allowing tab and shift+tab navigation
• adds toggle when pressing space, to simulate native keyboard toggling
• note: I didn't add any focus styles, so right now this uses native ones. not sure if you want to add some.
• fixes Keyboard support? #21

[euvl]

Hey! thanks for a PR! I will review it a bit later 👍
Quick question, it seems that there is no check whether component is focused or not (for space button click), does it need one?

[nelsonpecora]

No worries! I don't think it needs a check, since the keyboard event will only fire on that if it's focused (or if a child is focused, but it has no dynamic children), but I'm not 100% sure on that front.