ETT-1184 Add the columns toggle to user management tables

[moseshll]

• This adds the data-show-columns attribute to Approval Requests, Institutions, Registrations, and Users tables.
• The ticket did not call for Institutions, however I folded it in for consistency.
• Uses Table Cookie extension to persist hidden columns, and for good measure rows per page in the ht_downloads index page.
• Some minor formatting cleanup.
• No actual code changes, so no test changes.

Reviewer: this (minus the most recent commit [downloads rows-per-page cookification]) can be tested directly at https://preview.babel.hathitrust.org/otis (VPN required). The column show/hide doodly-doo looks like this:

and you should be able to accomplish column hidings that persist across reloads and navigation.

[coveralls]

coverage: 98.249% (+0.001%) from 98.248%
when pulling e864905 on ETT-1184_data-show-columns
into cf81157 on main.

[carylwyatt]

Preview was giving me a 404 for whatever reason, but I pulled this down locally and it looks good! I like the addition of the cookie to remember the user preference on the table columns. Do you think 7 days is long enough? If this is something Melissa is using this frequently, I might go 90-180 days so it's not as annoying to reset. Just a thought.

[moseshll]

@carylwyatt you know, that is the right thing to do, seven days is silly -- I think I will choose 90 days, but I want to extract that setting out into the config somewhere instead of just repeating a new value everywhere.