[SEARCH][FIX] Use error message from Vacancy::ERRORS for 404
[STORE] Added DELETE /vacancies/:id endpoint for deleting vacancies
[WIP][SEARCH] Added analyzers
[WIP][SEARCH] Changed function query definitions

* used custom random score generator based on document `updated_at` field and passed `seed` number;
  generated number is around 1 (for example something like 1.009987)

* `score_mode` used for combining computed scores for each function changed to `avg` to avoid negative score,
  which in combination with `boost_mode` `multiply` caused that score of whole document was negative
  (for example relatively high query score 3.14 with functions score -0.2 would return -0.628 (3.14 * -0.2) )