BibDocFile: register downloads with recid

* Adds self.recid when calling `register_download()`.
  (closes #1831) (closes #1832)

Signed-off-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
WebSearch: fix for 'rhs is of unknown type'

* Fixes TypeError in search_engine that was occurring when a new
  collection has been added but the webcoll has not yet been run.
  (closes #1819)

Signed-off-by: Sebastian Witowski <sebastian.witowski@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
mailutils: fix for send_email() error on DEV site

* For the DEV site `send_email()` function was failing while trying to
  concatenate list and string (because the CFG_SITE_ADMIN_EMAIL
  was not a list).  (closes #1744)

Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
Reviewed-by: Yoan Blanc <yoan.blanc@cern.ch>
BibIndex: move helper functions to utils file

* Moves some of the helper functions from bibindex_engine
  to bibindex_engine_utils file.

Signed-off-by: <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibIndex: WordTable API changes

* Removes 'fields_to_index' argument from WordTable's argument
  list.

Signed-off-by: <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibIndex: abstraction layer for terms retrieval

* Introduces new TermCollector class which
  handles terms retrieval from different
  part of the system.

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibIndex: indexing non-MARC standards

* Introduces NonMarcTermCollector for acquiring data
  from non-MARC records.

* Adds new column to tag table and inserts
  corresponding RecJson fields as another
  non-MARC value for 'tag'.

* Enhances test suite acordingly.

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibIndex: recjson fields in admin interface

* Admin interface shows recjson fields
  in logical fields overview.

* Fields and tags are shown directly in index
  overview.

* Edition of tag enhanced with option to
  change value for recjson field.

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>