[TASK] Performance improvement on indexing process

Use exec_INSERTmultipleRows instead of exec_INSERTquery for
submitting indexer results to table index_rel. This may save _a lot_
of I/O load, especially when a page contains many words to be indexed.

Skip words marked as stopWords to prevent flooding of index_rel table.

Resolves: #38742
Resolves: #18599
Releases: master
Change-Id: Ia729e6632124692cabe7d5ebe079db7d6795b809
Reviewed-on: http://review.typo3.org/20275
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>