add dash player to dash core components

[gvwilson]

#2338 started work on adding dash-player to dash-core-components; we should finish off that work.

[AnnMarieW]

The PR 2338 referenced above is just adding a prop to html.Video component. It is not adding dash-player as a dcc component.

I think it might be better to leave dash-player as a separate package.