Perform all request to db in a single thread to avoid blocking navmesh
generator threads due to slow write operations.
Write to db navmesh for all changes except update as it done for memory cache.
Batch multiple db operations into a single transaction to speed up writing by
not executing fsync after each insert/update query. All reads are performed in
the same transaction so they see uncommited data.
This AABB tree required when need to filter out input mesh that has not
influence navmesh tile output. This filtering is already done before. Each
recast mesh corresponds to a single navmesh tile and has appropriate bounds.
