Setup audio and video viewer support

__tests__/integration/mirador/video.html

src/components/AVViewer.js

src/components/AudioViewer.js

src/components/PrimaryWindow.js

src/components/VideoViewer.js

src/containers/AudioViewer.js

src/containers/PrimaryWindow.js

src/containers/VideoViewer.js

src/lib/MiradorCanvas.js

src/state/selectors/canvases.js