Migrate '.fa-spinner' to '.spinner' for 'app/views/projects/blob/viewers'

The old font awesome .fa-spinner class begun being migrated to our own .spinner class early in 2019.

Files in the directory mentioned in this issue's title still makes use of .fa-spinner by calling icon('spinner spin') and need to be migrated. This needs to happen in order to provide a consistent user experience.

If any problems are encountered while performing the migration, please raise them on the associated epic.