This changes the auth screens to use the modal-like style of the redesign.
This does not attempt to style the actual body content of each screen. Instead,
it covers the header area with logo, footer links, and overall modal container
only.
This component displays login and register buttons. It's currently used in the
composer when viewing a room as a guest.
The name is confusing because the login flow uses are very similarly named
`mx_Login_box` as a wrapping around forms, which is totally different than these
buttons.
Additionally, the components is moved to `views/auth` since it is very simple
and auth related.
