feat(website): Add ScrollbarWidget to OrthographicView example

[Pessimistress]

Change List

• Add ScrollbarWidget to https://deck.gl/examples/orthographic-view
• Add layer culling for better performance (draws ~8/188 layers at z=0 and 44/188 layers at z=-1)
• Fix docusaurus webpack resolution of css stylesheet

[coveralls]

coverage: 91.008%. remained the same
when pulling e6b8629 on x/ortho-example-update
into cf17618 on master.