MB-12852: Re-introduce _info handler

To get information about a spatial view group/design document there is
now the per node `_info` handler at
`/_spatial_view/bucketname/_design/designname/_info`. It should be used
for debugging purpose only as it is an expensive call.

Change-Id: I1102211653d4ed26ae40823a0db071a1df1cd1bc
Reviewed-on: http://review.couchbase.org/43960
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>