Started new API for handling data transformations.

The purpose of the new API is to be able to separate entities from
identities, so that the resolution process can be made much more
flexible, allowing to deal with corner cases like handling external
individuals which should be published in a URI relative to a managed
individual.

In addition, the new API will make a lot of emphasis on usability,
making it clear and easy to use altogether.
Clean-up refactorings to the new data API.
Refactored data transformation operations in the LDP4j Server Frontend
to facilitate integration of new data API.

Started refactoring EndpointController and OperationContext in the LDP4j
Server Frontend to hide implementation specific classes leaked from the
LDP4j Application Engine (Endpoint).
Updated version of the Javadoc plugin.
Revisited concurrency-control aspects of the new data API.
Temporarily remove new data API.
Added missing license header