MB-8241: Refactor couch_set_view_compactor module

Refactor all MapReduce View specific code out of the
couch_set_view_compactor module into the mapreduce_view
module.

Change-Id: Ia0ab6f47f79edf2ea1a4cb59f46011acffd67136
Reviewed-on: http://review.couchbase.org/26126
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>