[changed] css api, no more content/footer

- default button className is now `ic-modal-close`
  instead of `default` to avoid conflicts

- css isn't using flex box anymore because IE10
  and IE11's implementations don't support
  flexible columns appropriately yet (I am so sad)

- No longer need the `ix-modal-content` and
  `ic-modal-footer` components since we aren't
  attempting any css with them anymore
release v0.0.6