Omits norms and document frquency statistics from lucene documents

They are not used a.t.m. and removing them reduces disk space to 50%
from basic measurements.
Also the previous code added to node id fields ("id" and "_id_"),
which was also removed here.
Merge pull request #909 from tinwelint/2.0-lucene-stripped

Omits norms and document frquency statistics from lucene documents