increase localStorage page history variety

we already summarise lead keyword and section totals for the last 100 articles.

this is to add lead author, blog and series, as well as all the display names

The aim is so later we can use the info to show a "Jump-to" bar on the front based on what users like.

/cc @stephanfowler I'd love some feedback since it's your area of expertise =)
my bad. interesting, though hard to read, use of logical short circuiting. 
think this would make more sense to just return an object directly, but yep, can take a look together tomorrow