SES-1972 : Add test to manually verify that N-Triples is still legacy

TODO: Uncomment test when upgrading to RDF-1.1 N-Triples
SES-1972 : Regression numeric bnode identifiers N-Triples/N-Quads

Adds a new regression test to the standard RDFWriterTest for numeric
identifiers
SES-1972 : Ensure that blank nodes from NTriplesUtil start with letter

Check to ensure that blank node identifiers written using NTriplesUtil
start with a letter for backwards compatibility with RDF Test Cases
format.
SES-1972 : Return correct RDFFormat in NQuadsWriter
SES-1972 : Remove dashes from UUID bnode prefix in RDFParserBase
SES-1972 : Add regression test for blank node ids with dash in them
SES-1972 : Replace invalid BNode characters in NTriplesUtil

N-Triples, at least RDF Test Cases format, is strict about only
accepting letters and numbers as blank node identifiers, and only
letters as the first character. In order to satisfy this requirement,
the arbitrary BNode.getID() String values which can be setup by any
ValueFactory, must be validated, and any invalid characters overridden
when writing N-Triples and N-Quads.

The corner case of a BNode.getID() that is empty is also supported by
replacing it with a fixed value, as there is no other way of determining
its identity at this point.
SES-1972 : Add bnode fix to RDFParserBase.clear
SES-1972 : Call clear to reset bnode mappings in more parsers

Even though Rio parsers are not threadsafe, and are not designed to work
over multiple subsequent parses, if they incidentally work this way it
would be better to ensure, through the use of finally clauses, that
clear is called after each parse. This ensures that the bnode prefix is
reset each time.
Merged in SES-1972 (pull request #226)

SES-1972 : Fix regression from SES-1941 where numeric blank node identifiers are now present inside of the system
Merge branch '2.7.x' into SES-1960

Conflicts:
	core/rio/api/src/main/java/org/openrdf/rio/helpers/RDFParserBase.java