Added conditional checks to when `aria-label`, `role`, and `tabIndex`…

… get attached to `FlexTable` headers and rows.

These a11y properties are only added when on-click or sort handlers are present.

Added `aria-label` and `role` attributes to `FlexTable`, `Grid`, and …

…`VirtualScroll` components to fix a11y issues reported by [reactjs/react-a11y](https://github.com/reactjs/react-a11y).

Thanks to @globexdesigns for the contributions!

Separated horiontal and vertical `Grid` metadata calculation to avoid…

… unnecessarily recomputing row metadata for `FlexTable`s and `VirtualScroll`s when a browser's window is resized, for example.

Also replaced `columnWidth` and `rowHeight` getter uses in `Grid.render` in favor of cached cell metadata instead.

Small update to `FlexTable` to move the `rowGetter` call outside of t…

…he column loop to reduce the number of times that method gets called.

Added [transform-react-inline-elements](http://babeljs.io/docs/plugin…

…s/transform-react-inline-elements/) to UMD build for minor runtime performance improvements.

This change does not effect CommonJS or ES6 module builds because I did not want to remove prop-type checks.
You should apply this transformation step as part of your own production build pipeline.

Removed lingering references to `react-pure-render` with with [`shall…

…owCompare`](https://facebook.github.io/react/docs/shallow-compare.html).

This was meant to be part of the initial 6.0 release but was left out accidentally.

The primary purpose of this release is to improve customization and f…

…lexibility with regard to arrow-key event handling.

See CHANGELOG for backwards incompatible changes and upgrade path notes.

Max scroll position logic in `Grid` now takes scrollbar size into con…

…sideration.

Also includes a small `render` optimization for null cells.
This release made possible by @jquense!

Updated `package.json` to support React `^0.14.0` as well as `^15.0.0…

…-rc.1`.

Thanks to @opichals for the PR.

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.