Clean up #1337

[orenyk]

While dealing with merge conflicts for #1360 I caught some messy code from #1337:

1. We only include CsvExport in the CategoriesController, meaning that the index action with a zip format is probably broken for the EquipmentModelsController and the EquipmentItemsController.
2. Luckily, the links on all of the views for equipment export point to /categories.zip, so we're never hitting the routes for the other controllers.

We should be more consistent, either including it in all the controllers or just the one but then updating the index action in the others. @esoterik I'm giving this to you since the original issue was yours; sorry for not catching this earlier! We can wait for this until #1360 is finalized to avoid merge conflicts in the controllers.

[orenyk]

#1500 was merged in so I'm unblocking this @esoterik.

[zeffman]

looks good to me