Changed key-down event handler in `VirtualScroll`, `FlexTable`, and `Grid` to no longer call `event.preventDefault()` for arrow-key events.
This was causing poor user interactions for `<input>` elements within `VirtualScroll` and `FlexTable` components.
Note that this issue still occurs for `<input>` elements in a `Grid` component.

This release also removes the `outline: 0` default style for `Grid`.
After consideration I think that's a harmful default behavior.
