Add ability for exhibitions to link to viewing rooms on homepage

[saulshanabrook]

Currently, exhibitions on the home page have to link to the exhibition page. However, since things are now online mostly, there is an external viewing room site. We should have the link from the homepage link directly to the viewing room. Also, if you navigate to the exhibition from the exhibitions page or from an artist page, I think we should have a link on their to go to the viewing room?