LabelScanStore implementation that scales up to 137 billion labeled nodes

.. by using bitmaps in each document.

This implementation is configurable with 32bit bitmaps (68 billion nodes) or 64bit bitmaps (137 billion nodes).
The current default setting is to use 32bit bitmaps - it's a single line change to get 64bit bitmaps if we think we need that.

See previous discussions in https://github.com/neo4j/neo4j/pull/1285