adding titles and summaries to social media share links

I added parameters into the links instead of using Open Graph tags (og tags) as discussed with Dak. OG tags give us more control over what displays when shared, especially in Twitter. But, this is still a big improvement over what we have now.
It's not necessary to write a separate `getAbstract` method just to call `get('abstract')`.  Especially since this line is only being used here in the node model.