pylint and pep8 fixes to KWS

* now all files in keywordsearch package and kws_tests get >=9 in pylint
  -  removed old ugly ranker
  - refactored some code
* most of TODOs removed
*  some code may be still cleaned up further, but this will come later
* changes to DAS code:
  - src/python/DAS/utils/das_db.py: added get_db_uri() - returns default dburi from config