Force the start parameter to be a string

It appears that, when the 'start' parameter is a Fixnum, it does not 
get included in the params of the Rummager request. For now, explicitly 
converting this to a String fixes the issue. 

In the future, we might want to look at fixing this in API adapters, 
however given the work to fix the cruft in URL building (cc @elliotcm) 
it's probably not worth looking into right now.
Scope $searchResults to just the list of results

The #results container includes the filters and pagination links, and
so clicking the pagination links would fire the click tracking event
with a position of "1".

Scoping this to just the list of results seems a sensible fix.
Offset the click tracking number by the start value

This changes the search click tracking so that the result number takes 
pagination into account. 

It parses the value for the `start` URL parameter and adds it to the 
`position` variable.

If no `start` parameter is present, or if its malformed, it defaults 
to zero.