Add New Input Component

Based on the design in #2557, add or update the `Input` component and any dependencies of this component to the project. Feel free to use [this CodeSandbox](https://codesandbox.io/s/netlify-cms-editor-design-j1cg3) for reference.

> Note: Component should have both contained and inline states. Contained will have a border around the entire input. Inline will be as part of a form (such as the sign in form or editor form) with a single line underneath.

- [ ] Update or add component to project
- [ ] Add to Storybook
- [ ] Replace and use new component throughout project
- [ ] Write component tests
- [ ] Ensure tests pass
- [ ] Open a pull request