Allow customisation of the subject viewer for Talk

[eatyourgreens]

From Talk:

Making it so that volunteers have the same view in both the classifier and Talk would be very beneficial in all of the projects I moderate.

https://www.zooniverse.org/talk/14/114?comment=1110233&page=12

Talk for Ouroboros projects allowed customisation of the subject viewer on a per-project basis. PFE should allow project owners to change the global configuration for the subject viewer outside of workflow config settings.