Bugfix ensuring image download links correspond to currently displayed image...
Bugfix ensuring image download links correspond to currently displayed image in Mirador. Fixes DDK-319.
- Restores running feature specs locally with selenium/standalone-chrome Docker image
- Adds a custom DUL Mirador plugin to change the download links upon SET_CANVAS action
- Adds a 2-image Ad*Access item to the spec fixtures (TV0422) for JS tests
- Refines the data-manifest-url in the markup that Mirador reads so it's accurate in test env