Resolve "Fix the routing for wiki blobs"

Change the routing strategy for the wikis. Before we were setting the routing for project wikis and group wikis as the respective project_id and group_id. Now we have decided to use the routing as the root namespace id for both the Project wikis and the group wikis. This will simplify the group-level search. We don't need to send sub-group ids in the routing search. Closes #130 (closed)