Makes show page's availability async.

app/controllers/availability_indicators_controller.rb: adds a controller action to pull just a single document's availability and deliver it via partial.
app/views/catalog/_show.html.erb: provides a container for the partial instead of directly loading it, and adds AJAX to call the partial GET path.
app/views/catalog/_show_request_options.html.erb: reworks this partial to utilize the new variables coming from the just created action. Also adds script to open the show pages availability immediately.
app/views/catalog/show_tools/_metadata_block.html.erb: removes the exand command that wasn't working in this position anymore.
config/initializers/catalog_show_override.rb: Strips API reliant pulls from the Controller function.
config/routes.rb: adds another route to the AvailabilityIndicatorsController.

emory-libraries / blacklight-catalog