Contains a cascading list of search path templates, indexed by base object type.
Used by `Libraries::locate()` to perform service location. This allows new types of objects (i.e. models, helpers, cache adapters and data sources) to be automatically 'discovered' when you register a new vendor library or plugin (using `Libraries::add()`). Because paths are checked in the order in which they appear, path templates should be specified from most-specific to least-specific. See the `locate()` method for usage examples.