Material-sidenav tab order and focus needs to be handled

[marcysutton]

To be accessible, material-sidenav needs to hook into transition events to hide and show the component with display: none after animating. This will remove interactive controls from the tab order when they are not in use, which is easier and more performant than changing the tabIndex of every interactive child element.

In addition, focus should be sent into the sidenav when it opens, directing the user's attention to new content on screen. This helps a desktop keyboard user with a smaller screen, as well as a mobile screen reader user. The pattern is very similar to material-dialog.

[ajoslin]

Added display: none via 105b0e0.

[ajoslin]

Added focus via f66795e.

https://github.com/angular/material/blob/master/src/components/sidenav/sidenav.spec.js#L54-L61

[ajoslin]

Done!