only select first element in interactive div

This means for 'image' type interactive the caption
and credits won't be snapshotted. Currently Shutterbug
doesn't handle multiple element selectors very well.
It will set the size of each element to be the size 
of the first element. This creates lots of whitespace.

[#54415592]
https://www.pivotaltracker.com/story/show/54415592