UI design redo for exports

[saracarl]

After we've implemented -- and decide it's working for customers -- the new collection settings design, I'd like to see if we can use the same design pattern for the Export screens.

Here are the current 2 screens: http://localhost:3000/josie/ann-smith-letters/export http://localhost:3000/bulk_export/ann-smith-letters/new note that the bulk export screen has a "Previous Exports" section on it.

I suspect we could do a 3 part left sub-nav: Export Individual Works Bulk Export (or maybe Export Entire Collection) Previous Exports