Consistency checker: check that nodes are indexed.

o Directly use PropertyStore instead of the RecordAccess API
  to reduce code duplication at the expense of deferred check mechanism.
  This could prove to be an expensive check because of the need to read
  whole property chain for each node.
o Add parameters for turning off label scan store and index checks.
o Check uniqueness of unique indexes.
o Keep index accessors open for duration of entire consistency check.
o Extract tasks into their own class.
Consistency checker: use last committed transaction id as baseline for injected transactions.
Consistency checker: unwind nested test setup.
Merge pull request #1456 from apcj/2.0-ccheck-node-to-indexes

Consistency checker: check that nodes are indexed.