Add FallbackMode, URI Pattern and URI Prefix support to the DereferenceEngine

The generic implementation of the DereferenceEngine should be extended by the following options:

1. FallbackMode: If enabled it will not dereference Entities for those already some triples are present in the Enhancement Structure
2. URI Prefixes: Allows to configure prefixes of URIs that should be dereferenced
3. URI Patterns: Allows to configure regex pattern for URIs that should be dereferenced.

An Entity will only be scheduled for dereferenceing if

• !fallbackMode OR no triples are available
• prefixes.isEmpty() && patterns.isEmpty()
• the entity URI matches any of the prefixes or patterns

This allows to have multiple Engine instances with different field and ldpath configurations for different data sets (e.g. Geonames, DBPedia, SKOS, ...).

It also allows to avoid necessary calls Dereferencer that might need much more time to check if they can dereference an Entity.

By default fallback mode should be enabled, prefixes and patterns will be empty.