refactor ir index: class instead of globals

* use a class instance for IR index instead of functions with globals
* refactored IR index and chunk matcher
* use default /tmp/das as index dir if one not specified e.g. during build (merged with upmaster)
move kwd chunk matchers to proper place

* the whoosh folder was moved into entity_matchers.kwd_chunks
* renamed KWS/entity_matchers/result_fields_by_chunks.py into KWS/entity_matchers/kwd_chunks/chunk_matcher.py
  - so now it's nearby the related IR functions based on whoosh
rename the helper functions used for filtering kwd lists