Fixed issue #53.
Exceptions in converting statements now should result in the statement
to be skipped and a debug message to be logged.
Debug message is now more readable and catches all exception types.
Changed exception handling.
The following exceptions are caught:
* JSONException
* IllegalArgumentException
Remove wrong test
Remove unnecessary dependency
Merge remote-tracking branch 'origin/master' into fix-issue-#53

Conflicts:
	wdtk-dumpfiles/src/test/java/org/wikidata/wdtk/dumpfiles/JsonConverterTest.java

To accomodate for the data model changes.
Added the missing JsonConverterTest again.
No idea why this got lost.
Somehow, the changes in JsonConverterTest got lost, (also in master) so
here are the changes made during the introduction of snak groups.
Fix unit test
Merge pull request #54 from Wikidata/fix-issue-#53

Fix issue #53