Add Selected Databases access point.
Enable selected databases link on home page and databases access point masthead.
Abstract generic link logic into its own class.
Add index links mixin and include in SolrDocument.
Only show MARC 592 for databases.
Merge pull request #122 from sul-dlss/selected-databases

Add selected databases access point
Merge pull request #124 from sul-dlss/db-marc592

Only show MARC 592 for databases.
adds initial library locations access panel without hours api
adds hours request class and some tests

adds specs for integration and HoursRequest

updates constants and lib links

rescues Faraday connection and creates test config

test for null objects
adds updates to comments