MB-8029 Add view file sorter for incremental updates

To be invoked by couchdb, and tested through couchdb's
unit tests.

Change-Id: I6897a18d387f99a89a964274178d4a1e9d234d34
Reviewed-on: http://review.couchbase.org/25591
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>