Fix several issues with Datatables

[chrisvanrun]

This addresses several issues for the styling of Datatables

Closes #3745

Styling

The PR introduces a few custom CSS styles, overwriting some of the styles found in the bootstrap-4 extension of Datatables.

Leaderboard

The dom option is deprecated in Datatables. It had to be updated anyway to account for the new styling. This PR uses the new layout option in Datatables to set things up in a future-proof manner.

There are four states, as shown below.

Regular

Date & Additional Metrics

Date

Additional Metrics

Other

It also consolidates a few common settings in Datatables:

• Adds a default via-html-element-class selectable "nonSortable" column, employing it in one additional location.
• Sets the default paging size to 50 (most common).
• Sets the default type to "string" of client-side datatables, which indicates: do not transform content when searching/ordering. Also prevents unexpected styles from being applied because of 'automagically' detected content types.

[chrisvanrun]

Doing a final check-up:

• http://gc.localhost:8000/settings/api-tokens/

• http://gc.localhost:8000/challenges/costs/

• http://gc.localhost:8000/challenges/requests/

• http://gc.localhost:8000/components/interfaces/inputs/

• http://gc.localhost:8000/components/interfaces/outputs/

• http://demo.gc.localhost:8000/participants/registration/

• http://gc.localhost:8000/algorithms/test-algorithm/jobs/

• http://demo.gc.localhost:8000/evaluation/combined-leaderboards/overall/

• http://demo.gc.localhost:8000/evaluation/phase-1/

• http://demo.gc.localhost:8000/evaluation/phase-1/ground-truths/

• http://demo.gc.localhost:8000/evaluation/phase-1/leaderboard/

• http://demo.gc.localhost:8000/statistics/

• http://demo.gc.localhost:8000/participants/

• http://demo.gc.localhost:8000/participants/registration/

• http://demo.gc.localhost:8000/participants/registration/questions/

• http://demo.gc.localhost:8000/pages/

• http://gc.localhost:8000/reader-studies/reader-study/statistics/

• http://gc.localhost:8000/verifications/user-sets/1/

[chrisvanrun]

Kudos to James for having the hawkish eyesight to see the incongruent styling.

[chrisvanrun]

Also added a small tooltip for orderable headers. For instance, today I learned you can sort by multiple columns by holding Shift: