Port private file access token passing from UTSc fork

[alxp]

PR Forthcoming

The UT Scarborough fork of Islandora Mirador has code to pass along the Islandora token to enable Mirador to access non-public files if the user has access.

The fork is based on an older version of this module and the Javascript code has been refactored fairly significantly, including adding support for multiple Mirador instances on one page.

We should pull in the relevant changes, including a service worker that attaches the token to the thumbnail images.

This goes along with the currently open issues to support private file access for Islandora in OpenSeaDragon: Islandora/openseadragon#51 , Islandora/openseadragon#55