Update the Exhibition Guides index page

[gestchild]

Following #10821

Update the Exhibition Guides index page to more clearly signpost the different resources as well as the navigation between resources.

[LaurenFBaily]

FYI we have an upcoming instance of an exhibition (Kola Nuts, a temporary "display" in gallery 3) which will have a "captions" page but no audio/bsl highlight tour content. If it doesn't already, the index page will need to be able to just display the captions card. Hoping the work you're doing @gestchild to separate these out will make this straightforward.

[LaurenFBaily]

Dependent on #10914