Darcy ui i18 fundamental ui element types

I know the RadioButton naming isn't ideal but pushing this up to see if I'm heading in the right direction. I also have been working on darcy-webdriver to add implementations so I'll get that up here soon. Thank you!
Let's also add `check` and `uncheck`. Implementations can treat `click` like a toggle, and then `check` and `uncheck` will be useful for clients who don't care what the previous state was, they just know what they want the end state to be.