Move function to delete merged contacts to the Merger class and include all instances...

Move function to delete merged contacts to the Merger class and include all instances of the pair

The PrevNextCache class is a bit of a mess. It has 2 roles
1) be a cache
2) provide functionality specific to the Merger class

I am working to move this second functionality to the merger class and also to remove the cacheKey
filter on it. The cacheKey pertains to a particular search set. However if 2 people are deduping different search
sets and one person merges a contact pair they should not remain available in the other person's result set.

(Likewise, and to follow, if 2 contacts have a conflict we should update all search sets with that information,
not just the one that was actively being deduped)