Re-worked listings for days/weeks

- separated out the formatting of days and weeks into their own methods
to achieve the picks/articles split required
- Removing the use of channels/Toolbox::extractHighlightedArticle() to
sort picks from non-picks articles
- Retrieving a week article list will now only return articles with
is_picked = true
- Removed channels/Toolbox::extractHighlightedArticle()
- tidied up channel::getChannelListing() so it can now only be called
directly from an external route (previously callable from
channel::getSubChannel()