ATLAS: new `atlas-higgs-challenge-2014.xml`

* New records for the ATLAS Higgs Machine Learning Challenge 2014.
  (addresses #660) (PR #664)
docs: new file `atlas-higgs-challenge-2014.xml`

* (see PR #664)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
fixtures: new coll "ATLAS Higgs Challenge 2014"

* Adds new collection "ATLAS Higgs Challenge 2014".
  (closes #724) (see PR #664)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
ATLAS: Higgs Challenge 2014 MARCXML update

* Uses MARC field 505 to store information about CSV column
  semantics.  (To be completed.)  (addresses #728)

* Adds collection indicators for "regular" ATLAS collections.
  (addresses #660) (see PR #664)

* Moves evaluation matrix information into MARC field 500.
  (addresses #660) (see PR #664)

* Improves indentation of MARCXML records.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
ATLAS: addition of Higgs Challenge 2014 CSV file

* Adds CSV file for the Higgs Challenge 2014.
  (addresses #660) (see PR #664)

* Corrects file size in the record metadata.

* Amends installation instructions accordingly.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
records: addition of 505 to JSON data model

* Adds MARC field 505, representing CSV column semantics, to the JSON
  data model.  (addresses #728) (see PR #664)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>