simplify handlers
Use singleton list if only single annotation is used.
Use singleton sets for first value; switch if second value is added.
Do not ignore any round trip tests.
Don't force addMissingTypes to false for RDF Formats, whilst leaving it
set for others.
 (With JSONLD ignored), this reduces the number of failed tests from 26
to 14.

 With missing types added, there are 5 test cases with failures.
 Without missing types added, there are 8 test cases with failures.
Test negative data property value assertions that are xsd:string and PlainLiterals (currently fails for JSON-LD.
use Logger.trace for roundtrip test failures, easier to read when
debugging failing tests
Allow RDF Document formats to be both Prefix and non-Prefix aware.

Prefix Ontology Format Test Case now passes.
Extraneous restriction to Rio Prefix formats in method not under test.
Hasher, equality tester, and Trove custom hash strategery for comparing OWL Objects matching xsd:string to PlainLiteral with no language, and rdf:langString to PlainLiteral with lang tag.

New code used in round trip test.

JsonLD brought under test.

JSONLD marked as non-Prefix aware.
Remove overrides hiding possibly failing tests  - if a test  isn't passing, it should be seen to fail, or should be explicitly ignored.

 Ignorance isn't bliss.

 [oddly, some of the tests actually pass, and a few  RDF/XML renderings throw errors]
Use correctly formatted urns (maybe we ought to check for this).
Use correctly formatted urns (maybe we ought to check for this).
Address some of the roundtrip issues in #299

Tests still not all passing - the test change knocked off a manchester
syntax test, and the DataUnionOf test is still broken
Fix man syntax test failure. Still failing on DataUnionOf
When pushing triples from RIO Turtle parser to RDf consumer, 
blank nodes should have _: not #

Bit of a hack, really.
JSONLD makes plain literals into xsd:string literals

Adapted test to take this into account
Manchester syntax does not support GCIs - that was the reason for some
tests being ignored

It is now clear that the equal test in TestBase has become way too
complicated and format dependent. Needs thinking.
fix #299 roundtrip errors on TriX and various other syntaxes

The problem comes from the fact that these syntaxes have explicit blank
node ids outputted, where Turtle, for example, outputs [] nodes
repeating triples when structure sharing happens.
In TriX, duplicate triples are not emitted and shared structure is
outputted only once. On parsing, though, the triples get consumed the
first time they are found (which is expected behaviour, see reference),
and the second reference to the blank node does not have any triples
associated, hence the Error1 situation.

http://www.w3.org/TR/owl-parsing/#subsec-structure-sharing
OWLProfileViolationVisitorEx returns Optional<T> rather than nulls