CBD-612: Search algorithm for vtree

The vtree is now searchable with a list of
bounding boxes.

Change-Id: Icc17b6b5e71e8ca60373eccb72f861a956289135
Reviewed-on: http://review.couchbase.org/22334
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>