changed disable subject linking to enable for #2872

[sylvieed]

Resolves #2872

The problem

Previously, the "subject linking" / "subject indexing" toggle in the Collection settings page had a double negative, which is counterintuitive and confusing.

The solution

Changing the wording to "Enable subject linking" and flipping the boolean going to the database solves this.

Changes made

Previously, the check_boxes were using a value parameter to set their state. However, we found this parameter is not doing anything as check_boxes use the method passed to them to set their state. So, all uses of the value parameter in the collection/edit view were removed.

[coveralls]

Coverage decreased (-0.09%) to 79.848% when pulling 06ef17e on 2872-subject-linking-wording into 219c85e on development.

[benwbrum]

The tests are failing because the disable_subjects_spec is looking for the old wording. Changing that wording (and the click/unclick logic) around line 20 should fix them.

[benwbrum]

This looks good!