Support for label changes in index population

While the whole thing is TDD'd, we still need more tests to cover different scenarios, right now we test that adding a label to a node that already has properties properly gets indexed.

There is plenty of room to optimize this implementation as well, but that should IMHO be driven by need further down the road.

o Index completion now notifies index provider that the index has been p...
o Added proper handling of index creation failing.
o Implemented before/after snapshots for node records in logical log.
o Adding labels is now loads those properties and indexes them.