Enhanced the NIF for the first task

Fixed the NIF handling different problems:

URIs were not as descibed by the NIF standard (e.g., the "#char=X,Y" were missing)
added the begin and end indexes if they were missing
corrected the datatype of the indexes
added the correct way of referring to an entity mentioned by a string using itsrdf:taIdentRef
removed the dc:relation properties because they are not needed anymore

anuzzolese / oke-challenge