Adding hero to main.html allows for full width marketing images to be
used. This commit includes the addition of the hero block into
main.html along with the program marketing page's use of that new
hero block.
I wrongly assumed a video field wouldn't exist on a program
that doesn't include a video. Since it exists and is set to null
this fixes the retrieval of the source url.
This change adds the URL configuration and Django view required
to implement a program marketing page. It is left to theme builders
to implement a template that fulfills their own UX requirements.
WL-766
