MB-8241: Refactor couch_set_view module

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

Some other modules and the tests needed to be adapted
as well.

Change-Id: I8a060ce758704ecac4c949151b93288f1f825819
Reviewed-on: http://review.couchbase.org/26127
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>