fix kws web interface: use score instead of obsolete len_normalized_score

* earlier KWS refactoring removed it from KWS backend, but not from UI (removed in https://github.com/dmwm/DAS/commit/7a134d9a23bbe54a80426d0abbe94c5a4f237304#diff-ea7bd6177db0dfcdb23a1fbcbfd5cb41L106 )
- now in KWS UI we use 'score' instead of 'len_normalized_score'
* minor refactoring - use str.format