TNL-4906 Subsections now use radio buttons, to allow for "hide after due" as a
visibility option. Also, all tabs have been consolidated to "Basic" and
"Advanced", and visibility options have moved there.
Documentation links are updated to assist course authors with the new
visibility options. Tests have also been updated, and the changes suggested
in TNL-4951 are included.
1. Extract the full sentence rather than parital of a sentence, so that languages with different word orders than English can benifit from this.
2. Using ngettext instead of gettext with 'xxx(s)', as Transifex treats `()` as special characters so that it enforces the translated string must have the same number of `()` pairs. Such enforcement makes translations difficult, as not every language can use forms like 'xxx(s)' to represent both singular & plural within a single word.
