Add job title to fields accepted by coauthors

[benlk]

Changes

• Adds "Job Title" to the fields supported by Co-Authors Plus
• Adds the job title to the output of largo_byline if Co-Authors Plus is enabled
• Adds the job title to the output of largo_byline if Co-Authors Plus is not enabled
• Does not link the job title to the author's byline page
• Does not affect largo_author_link
• Adds the option to show a coauthor's email address. There doesn't appear to be a way to set a default, with how the metabox is constructed, so this will default to hiding the user's email address.
• Makes partials/author-bio-social-links.php respect the coauthors option. This will only affect coauthors users. This does not affect normal users; their email addresses will still display.

Why

For #1097 and WE-72.

[benlk]

This is a PR against master, because in discussions on #1097 it was determined that:

• this was needed for theme-wenews
• theme-wenews tracks the master branch of largo-dev
• this PR shouldn't affect other child themes or their websites

[benlk]

Additional changes (updated after 55a7a7b below):

• adds site-wide option to show or hide the job title, defaulting to hide
• adds job title to partials/author-bio-description.php, output as a p.job-title before the description.

A normal user in default Largo:

A guest author on theme-wenews:

[benlk]

After merging this, make sure to add these changes to the theme-wenews and theme-invw byline function.