Improve Fetching of Entity Information during the enhancement process

Short overview about the current Situation:

Previously the CachingDereferncingEngine was used do dereference information of Entities referenced in enhancement results. This engine loaded Entity data directly by using there IDs and stored the data in a Clerezza Graph. It was introduced before the Entityhub was implemented and was never updated to use the Entityhub.

STANBOL-333 removed the CachingDereferncingEngine and added support to dereference Entities via the Entityhub directly to the NamedEntityTaggingEngine.

However the removal of the CachingDereferncingEngine had the side effect that currently no other engine supports this feature. Engines must now support the fetching of entity data otherwise such data can no longer be provided.
In cases where multiple Engines support this features users would need to change the configuration for several engines in order to probably active/deactivate this feature. Activation/Deactivation for single requests would not be possible.

The proposal how to deal with fetching of entity information in future:

• Move the configuration for the default value to enable/disable dereferencing of Entity information to a central component (probably as a property of the EnhancerWebFragment)
• Add a possibility that allows users to override the default value for specific requests. This could use an additional parameter or also a HTTP header.
• Store the entity-dereference-state within the metadata of the Content-Item.
• If the entity-dereference-state is set to true EnhancementEngines MAY add entity information to the enhancement graph. This is especially useful if an engine does already fetch the required entity information during the enhancement process.
• To allow users to also fetch entity information that are not added during the enhancement process we might want to reintroduce a DereferenceingEngine that can dereference missing Entities. This engine MUST BE able to use the Entityhub with the option to also dereference Entities via there URI if they are not available via the Entityhub.

WDYT
Rupert