making Post Prominence tax items created via wp-admin visible on post add/edit screens

[rclations]

This PR is an update of #1252, but applied against the master branch as a hotfix

Fixes issue identified in #956

Prominence Terms added via /wp-admin/edit-tags.php?taxonomy=prominence are not displayed in the add/edit post screens.

This appears to be caused by the for loop that creates $termList in https://github.com/INN/Largo/blob/master/inc/post-metaboxes.php#L314

$largoProminenceTerms and by extension, $slugs only pull the default options set in the theme at https://github.com/INN/Largo/blob/master/inc/taxonomies.php#L90, so the for loop is only adding items to the display which exist in the default theme set.

I'm not sure if this loop was intended for something else, but removing it entirely and renaming $terms to $termList fixes the issue.

[benlk]

The failing test here is test_largo_fb_user_is_followable, which is known and was fixed with develop in #1234.