Add HathiTrust Emergency Temporary Access links via HT API and overlap file.

This ties the HT linking behavior to the HathiTrust Overlap file, which must be loaded into the application's database for links to work correctly. There is a rake task to support loading this data into the database.

The overlap file should be processed (possibly via this script: https://gist.github.com/corylown/7539ba5be9b84ad766ae49c94859d152) into a CSV with the following format:

oclc_number,bib_id,access
74,DUKE000000008,deny
75,DUKE000000009,deny
84,DUKE000000011,deny
105,DUKE000000012,allow
113,DUKE000000013,allow

Put this file into a location accessible by the application (such as /tmp) and run the following rake task:

rake dul_argon:hathitrust:reload_overlaps['/tmp/overlap_file.csv']