[bug 976711] Add source, campaign and organic facets

This adds "source", "campaign" and "organic" facets to the analyzer
search dashboard. In order to add these, I had to add some additional
fields to the mapping.

While doing that, I figured I'd add a "source :: campaign" composite
field which I'm not going to use now, but figured I'd use at some point
since it seems handy.

r?