Add option to exclude all labels

[nichtich]

This should speed up and avoid timeouts for very large hierarchies. Output in tree format could be like this:

http://www.wikidata.org/entity/Q634 •202 ×5 ↑
├──http://www.wikidata.org/entity/Q44559 •88 ×2961 ↑

in JSON format there would be no prefLabel and notation.

One-letter lowercase options available: -a, -g, -j, -k,-x, -y, -z.

Maybe -L, --no-labels?

By the way, the full class hierarchy contains more then 2 million statements so getting all would probably still not be possible.

[nichtich]

Implemented in the master branch, e.g. Q223557 (physical object) with > 85.000 classes can be queried with -Lb.